Haritha

KSEEB Solutions for Class 8 Science Chapter 18 Pollution Of Air And Water Points To Remember

Pollution: An undesirable change in the physical, chemical or biological characteristics of air, water and land that may be harmful to human life and other animals living conditions, industrial processes and cultural assets.

Pollutants: The agents that pollute our environment are called pollutants.
Pollutants are the substances which contaminate air, water, and land, For eg. smoke, dust fog and gases like sulphur dioxide and nitrogen dioxide. Air pollution is the contamination of air by impurities which may have a harmful impact on living organisms and non-living components.

Sources of Air Pollution:

Natural Sources: Smoke and dust arising from forest fires or volcanic eruptions. Methane gas arising from decaying organic matter, Man-made

Sources: Exhaust gases from factories, power plants and automobiles.

Carbon monoxide, nitrogen oxides, carbon dioxide, methane and sulphur dioxide are the major pollutants in the air. Smog is a mix in air of smoke and chemicals with fog. The chemical components of smog can include ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide. Smog can trigger breathing difficulties like asthma and coughing.

Steps to prevent air pollution:
Use of fuels like CNG and unleaded petrol in automobiles. Switching to alternative fuels, like solar energy, hydropower and wind energy.
Planting trees. Travelling to school on a bicycle or on public transport or carpooling. Avoiding the burning of leaves, trash and vegetable matter Restricting cigarette smoking. Increasing levels of greenhouse gases like CO, and CEC (Chlorofluorocarbon) are leading to global warming. Excessive use of CFCs damages the ozone layer which protects the earth from harmful UV rays emitted by the sun.

Greenhouse Effect and Global Warming:
The sun’s rays warm the earth’s surface. A part of the radiation that falls on the earth is absorbed by it and a part is reflected back into space. A part of the reflected radiation is trapped by the atmosphere due to the presence of gases like water vapour, carbon dioxide, methane, nitrous oxide etc known as greenhouse gases. This is known as the greenhouse effect.

The trapped radiations further warm the earth and have adverse effects such as the melting of glaciers and increasing sea levels. This phenomenon is
known as global warming.

Water pollution is the contamination of water by objectionable and harmful substances such as sewage, toxic chemicals, silt etc.

Sewage, agricultural chemicals and industrial waste are some of the major contaminants of water.

Water which is purified and fit for drinking is known as potable water. Water is a precious natural resource. We must learn to conserve it.

Class 8 Science KSEEB Pollution of Air and Water Notes 

Pollution Of Air And Water NCERT Textbook Exercises

Question 1. What are the different ways in which water gets contaminated?
Answer: Water gets contaminated due to the addition of substances harmful to health. Sewage, agricultural chemicals and industrial wastes are some of the major contaminants of water.

Question 2. At an individual level, how can you help reduce air pollution?
Answer: At an individual level we can help in reducing air pollution by following methods:
1. We can plant trees and nurture the ones already present in the neighbourhood.
2. We can take part in Van Mahotsava actively and effectively every year and motivate people about the importance of plantation.
3. We can educate people against burning dried leaves and plants and advise them to put them in a compost pit.

Question 3. Clear, transparent water is always fit for drinking. Comment
Answer: No clear and transparent water even without smell, may contain bacteria, viruses etc. which are not visible to the eyes. Drinking such water can cause illnesses of various kinds. Therefore, we must drink purified and potable water after boiling.

Question 4. You are a member of the municipal body of your town. Make a list of measures that would help your town to ensure the supply of clean water to all its residents.
Answer: The following steps could be taken:
1. First of all procurement of the required amount of water for all residents should be ensured.
2. Wastage of water by leakage at various places should be taken into account.
3. Water treatment should be ensured.
4. Must have sufficient water tanker to meet emergency situations.

Question 5. Explain the differences between pure air and polluted air.
Answer: Pure air is free from any pollutants has no smell, is soothing and not irritating to the eyes. Whereas polluted air gives a filthy smell and people cannot breathe in it. If people inhale such air, they may suffer from various breathing, heart and lung problems. Even sometimes people die from inhaling polluted air.

Question 6. Explain the circumstances leading to acid rain. How does acid rain affect us?
Answer: Gases like sulphur dioxide and nitrogen dioxide react with water vapour present in the atmosphere to form Sulphuric acid and nitric acid. These acids come down with rain water, making the rain acidic. This is known as acid rain. Acid rain corrodes the marble of the monuments. This phenomenon is known as Marble Cancer. It also kills the useful organism in agricultural soil.

Question 7. Which of the following is not a greenhouse gas?
1. Carbon dioxide
2. Sulphur dioxide
3. Methane
4. Nitrogen
Answer: 2. Sulphur dioxide.

Question 8. Describe the ‘Green House Effect’ in your own words.
Answer: The Sun’s rays when fall on the earth’s surface, get warm. Some of the Sun’s rays are trapped by the atmosphere and these and not allowed to go out of the earth’s atmosphere. This trapped heat cause warming of the atmosphere called the greenhouse effect. The gases like methane and carbon dioxide form a thick layer and prevent the escaping of heat causing this effect. Due to the greenhouse effect, global warming is happening.

Question 9. Prepare a brief speech on global warming. You have to deliver the speech in your class.
Answer:
1. Today, global warming has appeared as one of the most severe threats to human beings. On one hand, carbon dioxide is added to the atmosphere due to human activities. On the other hand, the forest area is decreasing day by day. It leads to an increase in the amount of carbon dioxide in the atmosphere. The accumulation of this gas causes the greenhouse effect and global warming.
2. Global warming can create the melting of ice of icebergs, resulting in a rise in the sea level and causing the flooding of many coastal areas. So, we must be aware of this problem and take every possible step to tackle it

Question 10. Describe the threat to the beauty of the ‘TajMahal
Answer: The Taj Mahal is made of white marble which is getting affected adversely due to the industrial pollutants from Agra, Mathura etc. the sulphur dioxide gas along with nitrogen oxide gas released from these industries mix with rainwater to form Sulphuric acid that falls on the marble of this monument. The acid rain corrodes the marble and makes it yellowish. This is a matter of great concern that world-famous monument like the Taj Mahal may get damaged due to the pollutants emitted by factories
around it.

Question 11. Why does the increased level of nutrients in the water affect the survival of aquatic organisms?
Answer: Agriculture relies on the use of chemical fertilizers to improve crop yield. All these chemicals dissolve in water and run into water bodies from the fields. These seep into the ground and pollute the groundwater. A lot of algae in the ponds grow and keep the ponds green. This is caused due to excessive quantities of chemicals like nitrates and phosphorous present in fertilisers. Excessive growth of algae decreases the oxygen level at water bodies and kills the other aquatic animals living inside it.

KSEEB Class 8 Science Solutions For Pollution of Air And Water 

Pollution Of Air And Water Activities

Question 1. You may have covered your nose while passing a brick kiln emitting smoke or started coughing while walking on a busy road

On the basis of your experience, compare the quality of air at the places given below: A park and a busy road.
A residential area and an industrial area.
A busy traffic intersection at different times of the day, e.g., early morning, afternoon and evening.
A village and a town.
Answer: When we visit a park we find it full of fresh air and on a busy road we find it polluted due to fumes, smoke, dust and sound.
An industrial area is more polluted as compared to a residential area as an industrial area gets polluted with chemical pollutants, toxic gases, etc. Early morning there is less pollution but in the afternoon it becomes a little more polluted than in the morning and in the evening it becomes extremely polluted. A town is more polluted than a village.

Question 2. Prepare a table using the pollutants mentioned above You may even add more data to the following Table
Answer:

Question 3. You have various options of commuting to your school such as walking, going by bicycle, travelling by bus or other public transport, using a car individually, travelling by carpool. Discuss in your class the impact of each of these options on the quality of air.
Answer:

Question 4. Try to collect samples of water from a tap, pond, river, well and lake. Pour each into separate glass containers. Compare these for smell, acidity and colour. Complete the following Table.
Answer:

Question 5. You investigated the sewage disposal system of your locality in Class VII. Do you remember how the sewage was collected from your home and where it went thereafter?
Answer: The underground network of small and big pipes called sewers carry the sewage from the point of production to the point of disposal, i.e., the treatment plant.

Question 6. Let us construct a water filter with simple, everyday materials.
Take a plastic bottle and cut it into 2 halves at the centre. Use the upper half as a funnel by putting it upside down in the lower half. Make layers in it with a paper napkin or a fine cloth followed by, cotton, sand and then gravel. Now pour dirty water through the filter and observe the filtered water.
Discuss the following questions amongst yourselves and with your teacher:
Why do we need to filter water before drinking?
Where do you get your drinking water from?
What will happen if we drink polluted water?
Answer:
1. Water which is full of dust particles and impurities is unfit for human health thus we need to filter water before drinking it.
2. We get drinking water from the government supply water or hand pump.
3. Polluted water has disease-carrying microorganisms and dissolved impurities which can make us seriously ill.

Pollution Of Air And Water Class 8 KSEEB Questions And Answers 

Pollution Of Air And Water Additional Questions

Question 1. What is the full form of CFC?
Answer: CFC — Chloro fluoro carbons

Question 2. What is meant by air pollution?
Answer: The presence of unwanted substances in the air which have a harmful effect on living and non-living components is known as air pollution.

Question 3. What name is given to unwanted substances present in the air?
Answer: Air pollutants.

Question 4. What are the harmful effects of smog?
Answer: Smog Causes breathing diseases such as asthma, cough and wheezing in children.

Question 5. How are CFCs added to the atmosphere?
Answer: CFCs are released from aerosol sprays, refrigerators and air conditioners.

Question 6. Name one important monument which has been affected by air pollution.
Answer: Taj Mahal is located in Agra.

Question 7. Expand SPM..,
Answer: Suspended Particulate Matter.

Question 8. Name some greenhouse gases.
Answer: Carbon dioxide, methane, nitrous oxide and water vapour.

Question 9. What is meant by polluted water?
Answer: Whenever substances such as sewage, toxic chemicals, silt, etc. which are harmful to life, get mixed with water, the water is said to be polluted.

Question 10. What is potable water?
Answer: Water which is suitable for drinking is called potable water.

Question 11. What is rain mixed with sulphuric acid called?
Answer: Acid rain.

Question 12. Name two smokeless fuels.
Answer: LPG and CNG.

Question 13. Name three diseases caused by polluted water.
Answer: Diarrhoea, dysentery and jaundice.

Question 14. What is Marble Cancer”?
Answer: Due to the acid rain the marble of the Taj Mahal has become yellow and is degrading. This is known as Marble Cancer”.

Question 15. Why is the greenhouse effect called so? How does it cause global warming?
Answer: It is called so because the earth’s atmosphere acts like a greenhouse made of glass in which sunlight enters through the transparent glass but the heat released by plants m the form of infrared radiation is not allowed to escape. Carbon dioxide does not allow heat to escape causing global warming.\

Explanation Of Pollution Of Air And Water In KSEEB Science 

Pollution Of Air And Water Multiple Choice Questions

Question 1. Air is a mixture of various gases. One of the gases is 21% part of the air and is essential for the survival of human beings. This gas is
1. Nitrogen
2. Oxygen
3. Ozone
4. Argon
Answer: 2. oxygen
Explanation: Nitrogen-78.09%
Ozone-0.000004%
Argon- 0.93%

Question 2. Which of the following is not a source of air pollution?
1. Automobile exhaust
2. Burning of firewood
3. Windmill
4. Power plant
Answer: 3. Windmill
Explanation: Windmill will not release any sort of gas into the atmosphere hence it is not considered a source of air pollution.

Question 3. Boojho wishes to contribute to reducing air pollution. Which vehicle should he use for going to school?
1. Car
2. School bus
3. Autorickshaw
4. Scooter
Answer: 2. School bus
Explanation: School buses carry many students hence reducing the emission. This will reduce air pollution.

Question 4. Which of the following is not a way to conserve water?
1. Replace
2. Reduce
3. Reuse
4. Recycle
Answer: 1. Replace
Explanation: Reduce, reuse and recycle is the formula to conserve natural resources. Replacement is not the way to conserve water.

Question 5. The type of pollution which is likely to affect the Taj Mahal in Agra to a greater extent is
1. Air pollution
2. Water pollution
3. Soil pollution
4. Noise pollution
Answer: 1. Air pollution
Explanation: Air pollution caused by residues from the nearby factory is causing damage to Tajmahal by converting white marble to yellow.

Question 6. Incomplete combustion of fuel such as petrol and diesel gives
1. Nitrogen oxide
2. Sulphur dioxide
3. Carbon monoxide
4. Carbon dioxide
Answer: 3. Carbon monoxide

Question 7. The phenomenon of marble cancer is due to
1. Soot particles
2. CFCs
3. Fog
4. Acid rain
Answer: 4. Acid rain
Explanation: Marble cancer is the phenomenon of corrosion of buildings and monuments due to the effect of acid rain.

Question 8. Potable water is the water which is
1. Obtained from a river.
2. Obtained from a lake.
3. Pure and fit for drinking.
4. Used only for washing clothes.
Answer: 3. Pure and fit for drinking.

Question 9. Which of the following procedures will give you water free from all impurities?
1. Adding chlorine tablets
2. Distillation
3. Boiling
4. Filtration
Answer: 2. Distillation

Question 10. A pond contains clean water. Which of the following activities will produce the least pollution of water?
1. Washing clothes in the pond
2. Animals bathing in the pond
3. Washing motor vehicles in the pond
4. Swimming in the pond.
Answer: 4. Swimming in the pond.

Question 11. Trees help in reducing the pollution of our environment. Lakhs of trees are planted by people in the month of July every year. The occasion is called
1. Forest Conservation Day
2. Plantation month
3. Van Mahotsav
4. wildlife week
Answer: 3. Van Mahotsav

Question 12. Which of the following is not a greenhouse gas?
1. Nitrogen gas
2. Water vapour
3. Methane gas
4. Carbon dioxide
Answer: 1. Nitrogen gas
Explanation: A gas that contributes to the greenhouse effect by absorbing infrared radiation is known as a greenhouse gas. Nitrogen is a part of atmospheric gases and it will not contribute to the greenhouse effect.

Question 13. Name the chemicals which are used in refrigerators and air conditioners and damage the ozone layer when released in the air.
Answer: Chlorofluorocarbons.

Question 14. Name any two sources which cause air pollution due to suspended particulate matter.
Answer:
1. Combustion of fuel
2. Industrial activities

Question 15. Name two gases which are mainly responsible for acid rain.
Answer:
1. Sulphur dioxide
2. Nitrogen dioxide

Question 16. The quality of air at various locations is monitored regularly by the government and other agencies? In what way can you use these data?
Answer: These data can be used to generate awareness about air pollution among people.

Question 17. The combustion of fossil fuels generates a lot of air pollution. Can you suggest any two alternative sources of energy which do not cause any pollution?
Answer: Solar energy and wind energy.

Question 18. Name any two water pollutants which are toxic for plants and animals.
Answer: Lead and Arsenic

Question 19. A lot of dry leaves are collected in a school garden and are burnt every day. Do you think that it is right to do so? If not, what should be done to dispose off the dry leaves?
Answer: Burning dry leaves is not the right thing to do as it causes air pollution. Converting dry leaves is the right thing to do as it does not cause any pollution and also gives manure.

Question 20. The level of air pollution is higher at a busy traffic intersections. Why?
Answer: Explanation: At traffic intersection automobiles stop for a while which lead to the accumulation of harmful gases at the junction. Hence the level of air pollution is higher at a busy traffic intersections.
Flow Chart

Karnataka State Board Syllabus for Class 8 Textbooks Solutions

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials: metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Conservation of Plants and Animals
• Chapter 7 Force and Pressure
• Chapter 8 Friction
• Chapter 9 Sound
• Chapter 10 Combustion and Flame
• Chapter 11 Cell Structure and Functions
• Chapter 12 Reproduction in Animals
• Chapter 13 Reaching the age of Adolescence
• Chapter 14 Chemical Effects of Electric Current
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water

KSEEB Solutions for Class 8 Science Chapter 14 Chemical Effects of Electric Current Point To Remember

Materials through which electric current can pass easily are called conductors of electricity. Electrical conductivity is a measure of the ability of a substance to allow the flow of an electric current.

Among solids, metals and graphite are good conductors of electricity and have high electrical conductivity. Some liquids are also good conductors. Pure water or distilled water is a poor conductor of electricity. But the presence of even a small amount of impurities(salts and minerals) makes water a good conductor as it contains ions through which conduction takes place.

Hence water from taps, wells, ponds, rivers, seas, lakes, etc. conducts electricity as they contain impurities. Most liquids that conduct electricity are solutions of acids, bases, and salts. When electricity is passed through a conducting solution, the molecules of the solution dissociate into ions. Ions are atoms or groups of atoms with a positive or negative charge.

These ions cause electrical conduction through the liquid. A liquid that conducts electricity due to the presence of ions is called an electrolyte.

Electrolysis:
1. The process of decomposition of a chemical compound in a solution when an electric current passes through it is called electrolysis. This process is due to the chemical effect of electric current.
2. Two electrodes are inserted in the solution and are connected to the terminals of a battery with a switch in between. This arrangement is called an electrolytic cell.
3. The electrode that is connected to the positive terminal of the battery is called the anode, and the other connected to the negative terminal is called the cathode.
4. Electrolysis is used in refining and extraction of metals from impure samples. This process is called electrorefining. It is also useful in coating one metal with another This process is called electroplating.
5. The passage of an electric current through a conducting solution causes chemical reactions. This is known as the chemical effect of electric current.

Some of the chemical effects of electric current are the following:
1. Formation of bubble of gas on the electrodes
2. Deposition of metal on electrodes
3. Change in colour of solutions

Electroplating:
1. The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.
2. The object to be electroplated is made the cathode (negative electrode) by connecting it to the negative terminal of the battery.
3. The metal which has to be deposited is made the anode (positive electrode) by connecting it to the positive terminal of the battery. The electrolyte is usually a salt solution of the metal to be coated.

Application of Electroplating:
1. Metals that rust are often coated with other metals to prevent rusting.
2. Chromium plating is found on bath taps car bumpers, etc. to give a bright attractive appearance and resist scratches and wear.
3. Silver plating is done on cutlery and jewellery items.
4. Tin cans, used for storing food, are made by electroplating tin onto the iron. Tin is less reactive than iron. Thus, food does not come into contact with iron and is protected from getting spoilt.

Class 8 Science KSEEB Chemical Effects Of Electric Current Notes 

Chemical Effects Of Electric Current NCERT Text Book Exercises

Question 1. Fill in the blanks.
1. Most liquids that conduct electricity are solutions of _____,_____and ____.
2. The passage of an electric current through a solution causes effects.
3. If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the _____ terminal of the battery.
4. The process of depositing a layer of any desired metal on another material by means of electricity is called _____

Answer:
1. Most liquids that conduct electricity are solutions of acids, bases and salts.
2. The passage of an electric current through a solution causes chemical effects.
3. If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the negative terminal of the battery.
4. The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.

Question 2. When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?
Answer: Yes, it is because the solution conducts electricity and the solution plays the role of the cell.

Question 3. Name three liquids, when tested in a manner that may cause the magnetic needle to deflect.
Answer: It may be the salt solution in water.

Question 4. The bulb does not glow in the setup List the possible reasons. Explain your answer?

Answer: The possible reasons are:
1. The solution may be conducting electricity but the current produced is too small so that the filament of the bulb does not get heated and the bulb does not glow.
2. It is possible that the connections are loose.
3. The cells are used up.

Question 5. A tester is used to check the conduction of electricity through two liquids. labelled A and B. it is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for liquid B. you would conclude that
1. Liquid A is a better conductor than liquid B
2. Liquid B is a better conductor than liquid A
3. Both liquids are equally conducting
4. Conducting properties of liquid cannot be compared in this manner.
Answer:
1. Liquid A is a better conductor than liquid B.

Question 6. Does pure water conduct electricity? If not, what can we do to make it conduct?
Answer: No. Pure water does not conduct electricity. This is because pure water is devoid of any salts. Pure water can conduct electricity when a pinch of common salt is added to it as the salt solution is conducting in nature.

Question 7. In case of fire, before the firemen use the water hoses, they shut off the main electric supply for the area. Explain why they do this.
Answer: Water may conduct electricity. If the electrical supply for the area is not shut off and water is poured over electrical appliances, then electricity may pass through the water and harm the firemen. That is why, in case of a fire, the firemen shut off the main electrical supply for the area before they use the water hoses.

Question 8. A child staying in a coastal region tests the drinking water and also seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason?
Answer: Impure water is the conductor of electricity. Sea water contains more impurities than drinking water found in the coastal region. Therefore, seawater conducts more electricity than drinking water. That is why the compass needle deflects more in the case of seawater.

Question 9. Is it safe for the electrician to carry out electrical repairs outdoors during heavy rain pour? Explain.
Answer: When it rains heavily, the rainwater dissolves many impurities from the atmosphere, which make it impure and very conductive of electricity. The air becomes humid with this water and becomes very conductive. That is why, it is not wise for an electrician to do electrical repair work when it rains heavily, because he may get dreadful shock or even gets an electric shock.

Question 10. Paheli had heard that rainwater is as good as distilled water. So, she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise, she found that the compass needle showed deflection. What could be the reason?
Answer: Rainwater is, of course, as good as distilled water but, when it passes through the atmosphere It dissolves a lot of dust dirt and impurities and becomes conducting. So, when Paheli used a tester, its compass showed deflection.

Question 11. Prepare a list of objects around you that are electroplated.
Answer: The objects which are electroplated are:
1. Taps of water connection.
2. Parts of the bicycle.
3. Body of cars, motorcycles and tractors.
4. Handles of the doors.

Question 12. The process is used for the purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?
Answer: The thick rod of impure copper should be attached to the positive terminal of the battery. This is because the free copper of the solution will get deposited on the thin rod and the loss of copper from the solution will be restored from the thick rod to the positive terminal of the battery. Thus, copper from the thick rod could be extracted.

KSEEB Class 8 Science Solutions For Chemical Effects Of Electric Current 

Chemical Effects Of Electric Current Activities

Question 1. Join the free ends of the tester together for a moment. This completes the circuit of the tester and the bulb should glow. However, if the bulb does not glow, it means that the tester is not working. Can you think of the possible reasons? Is it possible that the connections are loose? Or, the bulb is fused? Or, your cells are used up? Check that all the connections are tight. If they are, then replace the bulb with another bulb. Now test if the tester is working or not. If it is still not working then replace the cells with fresh cells.
Answer: In this activity, if the bulb does not glow, it means that either the connections of the circuit are loose or the bulb is fused or cells are used up. If the tester is working, it can be used to test the materials, i.e., whether it is a conductor or non-conductor of electricity.

Question 2. Collect a few small plastics or rubber caps of discarded bottles and clean them. Pour one teaspoon of lemon juice or vinegar into one cap. Bring your tester over this cap and let the ends of the tester dip into lemon juice or vinegar Take care that the ends are not more than 1 cm apart but at the same time do not touch each other. Does the bulb of the tester glow? Does lemon juice or vinegar conduct electricity? How would you classify lemon juice or vinegar—a good conductor or a poor conductor?

Answer: In this activity the bulb glows which shows that lemon juice and vinegar both conduct electricity, hence they are good conductors of electricity.

Question 3. Take the tray from inside a discarded matchbox. Wrap an electric wire a few times around the tray. Place a small compass needle inside it. Now connect one free end of the wire to the terminal of a battery. Leave the other end free. Take another piece of wire and connect it to the other terminal of the battery Join the free ends of two wires momentarily. The compass needle should show deflection. Your tester with two free ends of the wire is ready. Now repeat using this tester. Do you find a deflection in the compass needle the moment you dip the free ends of the tester in lemon juice?

Answer: Take out the ends of the tester from the lemon Juice, dip them in water and then wipe them dry. Repeat the activity with other liquids such as tap water, vegetable oil, milk, and honey. (Remember to wash and wipe the ends of the tester after testing each liquid). In each case observe whether the magnetic needle shows deflection or not.

Thus, lemon juice, vinegar, tap water, milk, curd and water, and soda are good conductors of electricity while vegetable oil, honey, kerosene oil, and distilled water are poor conductors of electricity or insulators.

Question 4. Take about two teaspoonfuls of distilled water in a clean and dry plastic or rubber cap of a bottle. (You may obtain distilled water from your school science lab. You may also get distilled water from a medical store or a doctor or a nurse). Use the tester to test whether distilled water conducts electricity or not. What do you find? Does distilled water conduct electricity? Now dissolve a pinch of common salt in distilled water. Again test. What do you conclude this time?
Answer: If the tester is put in distilled water, the bulb of the tester does not glow. This shows that distilled water does not conduct electricity. But when salt is dissolved in distilled water and again tested, the bulb glows which shows that water containing salts conducts electricity. Thus water which is free of salts is poor conductor while water with salts is a good conductor of electricity.

Question 5. Take three clean plastic or rubber caps of bottles. Pour about two teaspoonfuls of distilled water into each of them. Add a few drops of lemon juice or dilute hydrochloric acid to distilled water in one cap. Now in the second cap containing distilled water, add a few drops of a base such as caustic soda or potassium iodide. Add a little sugar to the distilled water in the third cap and dissolve it. Test which solutions conduct electricity and which do not. What results do you obtain?
Answer: First and second cap with acid and base respectively, conducts electricity whereas the third cap having sugar dissolved in distilled water does not conduct electricity.

Question 6. Take out carbon rods carefully from two discarded cells. Clean their metal caps with sandpaper. Wrap copper wires around the metal caps of the carbon rods and join them to a battery. We call these two-rod electrodes. (Instead of carbon rods, you may take two iron nails about 6 cm long.) Pour a cupful of water into a glass/ plastic bowl. Add a teaspoonful of salt or a few drops of lemon juice to water to make it more conducting. Now immerse the electrodes in this solution. Make sure that the metal caps of the carbon rods are outside the water. Wait for 3-4 minutes. Observe the electrodes carefully. Do you notice any gas bubbles near the electrodes? Can we call the change taking place in the solution a chemical change?

Answer: On passing an electric current through the conducting solution of lemon juice and water, a chemical reaction takes place. Water is dissociated into its constituent gases, ie., hydrogen and oxygen. Oxygen bubbles are formed on the electrode connected to the positive terminal of the battery and hydrogen bubbles are formed on the other electrode. Changes in the colour of solutions may occur depending on what solution and electrodes are used. This process is known as the chemical effects of current.

Chemical Effects Of Electric Current Class 8 KSEEB Questions And Answers 

Question 7. We will need copper sulphate and two copper plates of size around 10 cm x 4 cm. Take 250 ml. of distilled water in a clean and dry beaker. Dissolve two teaspoonfuls of copper sulphate in it. Add a few drops of dilute sulphuric acid to the copper sulphate solution to make it more conducting. Clean copper plates with sandpaper. Now rinse them with water and dry them. Connect the copper plates to the terminals of a battery and immerse them in copper sulphate solution.

Allow the current to pass for about 15 minutes. Now remove the electrodes from the solution and look at them carefully. Do you find any difference in any one of them? Do you find a coating over it? What colour is the coating? Note down the terminal of the battery with which this electrode is connected.

Answer: After removing the electrodes from the solution, we find that copper metal gets deposited on the plate at the negative of the battery. It is concluded that when an electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate. The free copper gets deposited on the plate acting as a cathode. Gradually, a layer of copper builds up on the plate. This process is known as electroplating.

Chemical Effects Of Electric Current  Additional Questions

Question 1. What are good conductors?
Answer: The substances that conduct electricity through them are called good conductors.

Question 2. Give four examples of insulators.
Answer: Air, wood, rubber and plastic.

Question 3. Name two metal objects which have a coating of another metal.
Answer: Handlebars of bicycles, bathroom taps.

Question 4. Is air a bad or good conductor?
Answer: A bad conductor.

Question 5. Which metal is plated on handlebars of cycles and the rim of wheels?
Answer: Chromium

Question 6. What is the full form of LED?
Answer: Light Emitting Diode.

Question 7. Which part of an atom is responsible for the flow of current?
Answer: Electron

Question 8. Why do most liquids conduct electricity?
Answer: Due to the presence of ions in them, most liquids conduct electricity,

Question 9. An LED is a more efficient device than a bulb. Why?
Answer: LED is more efficient because it can glow even when a weak or lost current flows through it.

Question 10. Do lemon juice or vinegar conduct electricity?
Answer: Yes, they conduct electricity.

Question 11. How is the conductivity of liquids tested?
Answer: By using a tester.

Question 12. Why is tin electroplated on iron to make cans used for storing food?
Answer: Tin is less reactive than iron. The tin coating prevents food from coming in contact with iron and thus prevents it from getting spoiled or corroded.

Question 13. What effect of current does electroplating show?
Answer: Chemical effect

Question 14. Which effect of current causes the bulb to glow?
Answer: Heating effect

Question 15. Name the three effects of electric current.
Answer: Heating, magnetic and chemical effects.

Question 16. How can the magnetic effect of current be checked?
Answer: By using a magnetic compass.

Question 17. What is electroplating?
Answer: The deposition of a thin layer of metal over another metal by electrolysis is called electroplating.

Question 18. What happens when an electric current is passed through the copper sulphate solution?
Answer: When an electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate. The free copper gets drawn to the electrode connected to the negative terminal of the battery and gets deposited on it.

Explanation Of Chemical Effects Of Electric Current In KSEEB Science 

Question 19. On what factors thickness of the electroplated items depend?
Answer:
1. Thickness of electroplated items depends upon:
2. The strength of the current passing through the circuit.
3. The concentration of the metal in the solution.
4. The duration of the time the article has been in the solution.

Question 20. With the help of a suitable diagram, explain the electrolytic refining of copper.
Answer: To purify copper, a thin plate of pure copper and a thick rod of impure copper are used as electrodes in the acidified solution of CuSO_4. Pure copper is used as a cathode and impure copper is used as the anode. When an electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate. The free copper gets drawn to the electrode connected to the negative terminal of the battery and gets deposited on it. From the impure copper electrode, an equal amount of copper gets dissolved in the solution. Thus, the loss of copper from the solution is restored and the process continues. The impurities are left behind at the anode.

Chemical Effects Of Electric Current Multiple Choice Questions

Question 1. An electric current can produce
1. Heating effect only.
2. Chemical effect only.
3. Magnetic effect only.
4. Chemical, heating, and magnetic effects.
Answer: 4. Chemical, heating, and magnetic effects.

Explanation:
1. Electric current causes a chemical reaction when it passes through a conducting solution. This is a chemical effect of electric current.
2. When an electric current passes through the bulb. Its filament gets heated and the bulb starts glowing. This is the heating effect of electric current.
3. When an electric current is passed through a circuit it produces a magnetic field around it. This is the magnetic effect of electric current.

Question 2. Boojho and Paheli performed experiments taking similar bulbs and cells but two different solutions

They found that the bulb glows more brightly as compared to that You would conclude that
1. Higher current is flowing through the circuit
2. Higher current is flowing through the circuit
3. Equal current is flowing through both circuits.
4. The current flowing through the circuits in the two setups cannot be compared in this manner.

Answer: 1. Higher current is flowing through the circuit
Explanation: Higher current is flowing through the circuit

Question 3. Boojho’s uncle has set up an electroplating factory near his village. He should dispose of the waste from the factory
1. In the nearby river.
2. In the nearby pond.
3. In the nearby cornfield.
4. According to the disposal guidelines of the local authority.

Answer: 4. According to the disposal guidelines of the local authority.
Explanation: Waste disposal is a major concern in the electroplating industry as it causes water pollution and releases a hazardous chemicals into water bodies. Hence it should be disposed of according to the guidelines of the local authority.

Question 4. When an electric current is passed through a conducting solution, there is a change of colour of the solution. This indicates
1. The chemical effect of current.
2. The heating effect of current.
3. The magnetic effect of current.
4. The lightning effect of current.

Answer: 1. The chemical effect of current
Explanation: Conducting a solution through electric current cause’s chemical reaction. This causes a change in colour and this is the chemical effect of electric current.

Question 5. Which one of the following solutions will not conduct electricity?
1. Lemon juice
2. Vinegar
3. Tap water
4. Vegetable oil

Answer: 4. Vegetable oil
Explanation: Vegetable oil does not contain ions hence it cannot conduct electricity.

KSEEB Class 8 Science Chapter 14 Important Questions 

Question 6. Which of the following metals is used in electroplating to make objects appear shining?
1. Iron
2. Copper
3. Chromium
4. Aluminium

Answer: 3. Chromium
Explanation: Chromium metal is used in electroplating to make objects appear shining because chromium has shining properties and is scratch resistant.

Question 7. Which of the following solutions will not make the bulb glow?
1. Sodium chlorides
2. Copper sulphate
3. Silver nitrate
4. Sugar solution in distilled water
Answer: 4. Sugar solution in diluted water
Explanation: The sugar solution is neither acidic nor basic and it cannot ionize to conduct electricity. Similarly, distilled water has no ions in it to conduct electricity. Hence the mixture of sugar solution and distilled water will not conduct electricity.

Question 8. Fill in the blanks
1. The object to be electroplated is taken as ______electrode.
2. One of the most common applications of the chemical effect of electric current is ________
3. Small amount of mineral salt present naturally in water makes it a ______ of electricity.
4. Electroplating of  _________is done on objects like water taps and cycle bells to give them a shiny appearance.

Answer:
1. Cathode
2. Electroplating
3. Conductor
4. Chromium

Question 9. Why is a layer of zinc coated over iron?
Answer: Tron readily reacts with atmospheric air to form rust. In order to prevent it from rusting zinc is coated over iron.

Question 10. Will the solution of sugar in distilled water conduct electricity?
Answer: No, the sugar solution is neither acidic nor basic and it cannot ionize to conduct electricity.

Question 11. Name the effect of current responsible for the glow of the bulb in an electric circuit.
Answer: Heating effect of electric current.

Question 12. Boojho made the circuit given and observed that the bulb did not glow. On Paheli’s suggestion, he added one more cell in the circuit. The bulb now glows. Explain.

Answer: On adding another cell current flows through bulb sufficiently to make it glow.

Question 13. Paheli set up an experiment using liquid A in the beaker She observed that the bulb glows. Then she replaced the liquid A by another liquid B. This time the bulb did not glow. Boojho suggested replacing the bulb by an LED. They observed that the LED glows. Explain.

Answer: The current flowing through liquid B may be weak to make the bulb glow whereas it was strong enough to make the LED glow.

Simplified Notes For KSEEB Class 8 Science Electric Current 

Question 14. Paheli wants to deposit silver on an iron spoon. She took a silver nitrate (AgNO3) solution in a beaker and set up a simple circuit for electroplating. Which terminal of the battery should the spoon be connected to? What material should the other electrode be made of?
Answer: The spoon should be connected to the negative terminal of the battery. The other electrode should be made of silver.

Question 15. Why is tin electroplated on iron to make cans used for storing food?
Answer: Tin is less reactive than iron. In order to prevent iron from reacting with food, tin is coated over iron for storing food.

Question 16. Which of these two circuits A or B shows the correct observation?
Answer:

Karnataka State Board Syllabus for Class 8 Textbooks Solutions

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials: metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Conservation of Plants and Animals
• Chapter 7 Force and Pressure
• Chapter 8 Friction
• Chapter 9 Sound
• Chapter 10 Combustion and Flame
• Chapter 11 Cell Structure and Functions
• Chapter 12 Reproduction in Animals
• Chapter 13 Reaching the age of Adolescence
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water

KSEEB Solutions for Class 8 Science Chapter 16 Light Points To Remember

Light: The natural agent that stimulates sight and makes things visible. Light is reflected from all surfaces. It is a form of energy.
Objects that give out light on their own are called luminous objects.
Objects that do not give out light on their own are called non-luminous objects.

Reflection of Light: Bouncing back of light after striking a shiny or polished surface, in the same medium, is called reflection.
Types of Reflection:
1. Regular Reflection: When a beam of parallel light rays is incident on a smooth and plane surface, the reflected rays will also be parallel. This type of reflection is called Regular Reflection. The reflection from a plane mirror is an example of regular reflection.
2. Diffused or Irregular Reflection: When light is incident upon a rough or uneven surface, it is reflected in many directions due to the presence of irregularities on that surface.

If a reflected light ray is reflected again on being incident on another surface, it is termed multiple reflection. Multiple reflections are used in periscopes. Periscopes are used in submarines, war tanks, and by soldiers in bunkers to see objects that are not visible directly. In a kaleidoscope, beautiful patterns are formed due to multiple reflections.

Laws of reflection:
1. The angle of incidence is equal to the angle of reflection.
2. Incident ray reflected ray, and the normal drawn at the point of incidence to the reflecting surface, lie in the same plane.
3. Lateral inversion is the effect produced by a plane mirror in reversing images from left to right. For e.g. our left hand will appear as right and vice versa.

The image formed by a plane mirror is:
1. Of the same size as that of the object
2. Left-right inverted
3. Erect and virtual
4. Formed behind the mirror at the same distance as the distance the object in front of the mirror

Two mirrors inclined to each other give multiple images. Sunlight is called white light; consists of seven colors. The splitting of light into its constituent colors is known as dispersion. Visually challenged persons can read and write using the Braille system.

Parts of the Human Eye:
1. Cornea: Transparent bulge on the front surface of the eyeball which protects the eye and helps in the refraction of light.
2. Lris: Coloured diaphragm behind the cornea which controls the amount of Light entering the eye.
3. Pupil: Dark hole in the middle of the iris through which light enters the eye.
4. Eye lens: Transparent, crystalline structure behind pupil and iris.
5. Ciliary muscles: Hole in the eye lens in position and control the focal length of the eye lens.
6. Retina: The surface of the rear part of the eyeball where the light entering the eye is focused.
7. Rods and Cones: Rod cells respond to the brightness of light while cone cells respond to colours.
8. Blindspot It is the least sensitive point where no rods and cones are present.
9. The space between the cornea and the eye lens is filled with aqueous humor.
10. The space between the eye lens and the retina is filled with vitreous humor.

Class 8 Science KSEEB Light Chapter Notes 

Light NCERT Textbook Exercises

Question 1. Suppose you are in a dark room. Can you see objects in the ream? Can you see objects outside the room? Explain.
Answer: We cannot see objects in dark rooms. But we can see objects outside the room, in case there is a light outside the room. To see an object needs light which must reflect from the object to the eyes.

Question 2. Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?
Answer:
Regular reflection
1. The reflected rays are parallel to incident rays.
2. It occurs when an incident ray falls on a smooth or polished surface.
Diffused reflection
1. The reflected rays are not parallel to incident rays.
2. It occurs when an incident falls on a rough surface. No, diffused reflection is not the failure of the laws of reflection.

Question 3. Mention against each following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.
1. Polished wooden table
2. Chalk powder
3. Cardboard surface
4. Marble floor with water
5. Mirror
6. Piece of paper.
Answer:
1. Regular reflection will occur because of the polished surface.
2. Diffused reflection will take place because it is a rough surface.
3. Diffused reflection will take place because it is not a polished surface.
4. Diffused reflection will take place because marble and water will form a prism.
5. Regular reflection takes place because a plane mirror is a polished surface.
6. Diffused reflection due to rough surface.

Question 4. State the law of reflection.
Answer: The laws of reflection are
1. The angle of the incident is equal to the angle of reflection.
2. The ray of incidence, ray of reflection, and normal to-the-point incidence lie in the same plane.

Question 5. Describe an activity to show that the incident ray, the reflected ray, and the normal at the point of incidence lie in the same plane.
Answer:
Material required: a white sheet of paper, a drawing board, drawing pins, and a comb.
Procedure:
1. A white sheet of paper on a drawing board is fixed.
2. A strip of plane mirror is taken and placed in the path of the light ray.
3. The ray of light will be reflected.
4. Angle of incidence and angle of reflection on the sheet of paper is drawn,
5. The incident and reflected rays along the paper is observed. Now the sheet of paper is bent a little at the position of the reflected lay.
6. Keeping the incident ray and the normal in the plane of the drawing board, the reflected ray is tried to be seen now
Observation: The incidence ray, reflected ay, and normal lie in the same plane.

Question 6. Fill in the blanks in the following.
1. Person 1 min front of a plane mirror seems to be 2m away from this image.
2. If you touch your left ear with a right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with your left hand.
3. The size of the pupil becomes large when you see in dim light.
4. Night birds have less cones than rods in their eyes.

Question 7. The angle of incidence is equal to the angle of | Ans: Laser torch can harm or even damage the eye. So,reflection.
1. Always
2. Sometimes
3. Under special conditions
4. Never
Answer: 1. Always.

Question 8. The image formed by a plane mirror is
1. Virtual, behind the mirror and enlarged
2. Virtual, behind the mirror and of the same size as the object
3. Real at the surface of the mirror and enlarged
4. Real, behind the mirror, and of the same size as the object
Answer: 2. Virtual, behind the mirror and of the same size as the object.

Question 9. Describe the construction of a kaleidoscope.
Answer: A kaleidoscope is an optical instrument used to see a number of beautiful patterns. It is made up of a circular cardboard tube or tube of thick chart paper in which rectangular mirror strips are joined together to form a prism. At one end of the tube, touching these mirrors, a circular glass plate is fixed, Several small pieces of colored glass are placed upon it. This end is closed by a ground glass plate and beautiful patterns are seen through the other end of the kaleidoscope.

KSEEB Class 8 Science Solutions For Light 

Question 10. Draw a labeled sketch of the human eye.
Answer:

Question 11. Gurmit wanted to perform using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teacher’s advice?
Answer: Laser torch can harm or even damage the eye. So her teacher advised her not to do so.

Question 12. Explain how you can take care of your eyes.
Answer: The following care should be taken to keep our eyes healthy:
1. We should not look at the sun or a powerful light source directly.
2. Too light too much light is bad for the eyes.
3. If advised, suitable spectacles should be used.
4. We should always read from a normal distance for distinct vision.
5. We should never rub our eyes if any small particle or dust goes into the eyes.
6. Food containing Vitamin A should be used.

Question 13. What is the angle of incidence of a ray if the reflected rays are at an angle of 90 degrees to the incident?
Answer: The angle of incidence is 45°

Question 14. How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?
Answer: Infinite number of images of the candle will be formed if it is placed between two parallel plane mirrors.

Question 15. Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° Draw the reflected ray from the second mirror.

Answer:

Question 16. Boojho stands at A just on the side of a plane mirror Can he see himself in the mirror? Also, can he see the image of objects situated at P, Q, and R?

Answer: No, Boojho can’t see himself in the mirror. He can see the image of the object at P and 0 but not of R.

Question 17.
1. Find out the position of the image of an object situated at A in the plane mirror
2. Can Paheli at B see this image?
3. Can Boojho at C see this image?
4. When Paheli moves from B to C. where does the image of A move?

Answer: It is shown in the following picture.

1. Yes, Paheli can see the image of A.
2. Yes, Boojho can see the image of A.
3. Image of the object at A will not move as an object is not moving.

Light Class 8 KSEEB Questions And Answers 

Light Activities

Question 1. Fix a white sheet of paper on a drawing board or a table. Take a comb and close all its openings except one in the middle. You can use a strip of black paper for this purpose. Hold the comb perpendicular to the sheet of paper. Throw light from a torch through the opening of the comb from one side With a slight adjustment of the torch and the comb you will see a ray of light along the paper on the other side of the comb. Keep the comb and the torch steady. Place a strip of the plane mirror in the path of the light ray What do you observe?

Answer: It is observed that after striking the mirror, the ray of light is reflected in another direction.

Question 2. Perform again. This time use a sheet of stiff paper or chart paper. Let the sheet project a little beyond the edge of the Table Cut the projecting portion of the sheet in the middle. Look at the reflected ray. Make sure that the reflected ray extends to the projected portion of the paper. Bend that part of the projected portion on which the reflected ray falls. Can you still see the reflected ray? Bring the paper back to its original position. Can you see the reflected ray again? What do you infer?

Answer: Yes, the reflected ray of light is seen on the sheet. It is concluded that the entire sheet fixed on the drawing board represents a plane. The incident reflected rays and the normal lie in the plane of the paper.

Question 3. A source of light 0 is placed in front of a plane mirror PQ. Two rays OA and OC are incident on it Can you find out the direction of the reflected rays? Draw normals to the surface of the mirror PQ, at points A and C. Then draw the reflected rays at points A and C. How would you draw these rays? Call the reflected rays AB and CD, respectively. Extend them further. Do they meet? Extend them backward. Do they meet now? If they meet, mark this point as I. For a viewer’s eye at E do the reflected rays appear to come from point ? Since the reflected rays do not actually meet at I, but only appear to do so, we say that a virtual image of the point O is formed at I. As you have learned already in Class VII, such an image cannot be obtained on a screen.

Answer: An image formed by a plane mirror cannot be obtained on a screen. Thus, the plane mirror forms a virtual image.

Question 4. Imagine that parallel rays are incident on an irregular surface Remember that the laws of reflection are valid at each point of the surface. Use these laws to construct reflected rays at various points. Are they parallel to one another? You will find that these rays are reflected in different directions.

Answer: It is observed that the reflected rays are not parallel to each other due to irregularities in the reflecting surface. This type of reflection is known as diffused or irregular reflection.

Question 5. Take two plane mirrors. Set them at right angles to each other with their edges touching To hinge them you can use adhesive tape. Place a coin in between the mirrors. How many images of the coin do you see?

Now hinge the mirrors using the adhesive tape at different angles, say 45°, 60°, 120°, 180°, etc. Place some object (say a candle) in between them. Note down the number of images of the object in each case. Finally, set the two mirrors parallel to each other. Find out how many images of candles placed between them are formed
Answer:
1. When two plane mirrors are joined at right angles, then three images are formed.
2. When two plane mirrors are joined at 45°, 7 images are formed.
3. When two plane mirrors are joined at 60°, 5 images are formed.
4. When two plane mirrors are joined at 120°,2 images are formed.
5. When two plane mirrors are joined at 180°,1 image is formed.
6. When the plane mirrors are parallel to each other, infinite images are formed.

Question 6. To make a kaleidoscope, get three rectangular mirror strips each about 15 cm long and 4 cm wide. Join them together to form a prism Fix them in a circular cardboard tube or tube of thick chart paper. Make sure that the tube is slightly longer than the mirror strips. Close one end of the tube with a cardboard disc having a hole in the center, To make the disc durable, paste a piece of the transparent plastic sheet under the cardboard disc. At the other end, touching the mirrors, fix a circular plane glass plate Place on this glass plate several small pieces of colored glass (broken pieces of colored bangles). Close this end of the tube with a ground glass plate. Allow enough space for the color pieces to move around.

Answer: A variety of patterns are observed in the tube. Kaleidoscope operates on the principle of multiple reflections.

Explanation Of Light In KSEEB Class 8 Science 

Question 7. Get a plane mirror of a suitable size. Place it in a bowl (Katori) Fill the bowl with water. Put this arrangement near a window in such a way that direct sunlight falls on the mirror. Adjust the position of the bowl so that the reflected light from the mirror falls on a wall. If the wall is not white, fix a sheet of white paper on it. The reflected light will be seen to have many close their right eye. Look at the round mark now and repeat the activity. Does the cross-colors. How can you explain this?

Answer: The mirror and water form a prism and breaks up the light into its colors. The splitting of light into its colors is known as the dispersion of light. A Rainbow is a natural phenomenon showing dispersion.

Question 8. Look into your friend’s eye. Observe the size of the pupil. Throw light on her eye with a torch. Observe the pupil now. Switch off the torch, and observe her pupil once again. Do you notice any change in the size of the pupil? In which case was the pupil larger? Why do you think it was so? In which case do you need to allow more light in the eye, when the light is dim or bright?
Answer: When the light from the torch falls on the pupil, its size becomes smaller to allow less amount of light to enter the retina. When light is switched off, the pupil enlarges to allow more light to enter the retina. Thus, the pupil controls the amount of light entering the eye.

Question 9. Make a round mark and a cross on a sheet of paper with the spot to the light of the cross. The distance between two marks may be 6- 8 cm. Hold the sheet of paper at an arm’s length from the eye. Close your left eye. Look continuously at the cross. Move the sheet slowly towards you, keeping your eye on the cross. What do you find? Does the round mark disappear at some point? Now close your right eye. Look at the round mark now and repeat the activity. Does the cross disappear?

Answer: Yes, the cross disappears. The disappearance of the cross or the round mark shows that there is a point on the retina which cannot send messages to the brain when light falls on it.

Question 10. Get a square piece of cardboard of size 6-8 cm. Make two holes Thread a string through the two holes. Draw/paste a cage on one side of the cardboard and a bird on the other side. Twist the string and make the card twirl rapidly. Do you see the bird in the cage?

Answer: Yes, we can see the bird in the cage. Thus, the impression of an image persists in the retina for about 1/16th of a second.

KSEEB Class 8 Science Chapter 16 Important Questions 

Light Additional Questions

Question 1. Define dispersion of light.
Answer: Splitting up white light into seven colors when it passes through a glass prism is known as the dispersion of light.

Question 2. Name the colors in the order they appear in the spectrum of light.
Answer: VIBGYOR — Violet, Indigo, Blue, Green, Yellow, Orange, and Red.

Question 3. What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?
Answer: The angle of incidence = 45°

Question 4. What are the two factors responsible for an object being seen?
Answer: To be seen as an object, the sense of vision and light are required.

Question 5. What are illuminated objects?
Answer: Objects which reflect the light falling on them and can be seen are known as illuminated objects

Question 6. What is white light?
Answer: Sunlight is a mixture of seven colors also known as white light.

Question 7. Give one example of natural dispersion.
Answer: Formation of the rainbow.

Question 8. Which kind of spherical mirrors are used in vehicles? Why?
Answer: A convex mirror is used in vehicles because it gives the driver a large field of view.

Question 9. Why is it important to take care of our eyes? Mention any two activities that may cause damage to our eyes.
Answer: Eyes are the most wonderful gift of nature to us and they must serve us for our whole life. Our eyes can be damaged by playing carelessly or by hurting them with sharp projections

Question 10. Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room? Explain.
Answer: The objects cannot be seen inside the room because there is no light. The objects outside the room can only be seen if there is light outside.

Question 11. Distinguish between real and virtual images.
Answer: Differences:
Real image
1. The rays actually meet at a point.
2. The image can be obtained on a screen.
Virtual image
1. The rays do not meet at a point.
2. The image cannot object obtained on a screen.

Question 12. What is color blindness? Give a reason for this defect.
Answer: Some people cannot distinguish between the different colors. This is known as color blindness. Colour blindness is due to the absence of cones on the nerve endings on the retina.

Question 13. What are cones and rods? What are their functions?
Answer:
1. Cones are nerve endings that are sensitive to color light. They help us to distinguish between colors.
2. Rods are nerve endings that are sensitive to bright light.

Question 14. How do visually impaired people communicate?
Answer: Visually impaired people can communicate by following methods
1. By using the Braille system which employs groups of dots to represent printed letters and numbers.
2. In 1980, Braille computer software was developed. It can input, output, and translate documents to and from Braille.
3. By speech technology that can convert ordinary text into speech.

Question 15. Give some uses of plane mirrors.
Answer: Plane mirrors are used for dressing up, shaving beards, in scientific meters, and far designing periscopes.

Detailed Notes On Light KSEEB 

Light Multiple Choice Questions

Question 1. Part of the eye which controls the light entering is called
1. Iris
2. Cornea
3. Lens
4. Retina
Answer: 1. Iris
Explanation: Iris is a dark muscular structure that exists behind the cornea. Its function is to control the entry of light.

Question 2. We can see a non-luminous object when light:
1. Emitted by the object falls on the eye.
2. Is reflected from the object towards our eye.
3. Completely passes through the object.
4. Gets completely absorbed by the object.
Answer: 2. Is reflected from the object towards our eye.

Question 3. Light falling on surfaces S1, S2, and S3 Surfaces on which the angle of incidence is equal to the angle of reflection is/are
1. S1 only
2. S1 and 82 only
3. S2and $3
4. All the three surfaces

Answer: 4. All the three surfaces
Explanation: Laws of reflection are always followed irrespective of the surface of the object hence the angle of incidence is equal to the angle of reflection.

Answer 4. A tiny mirror M is fixed on a piece of cardboard placed on a table. The cardboard is illuminated by light from a bulb. The position of the eye with respect to the position of the bulb as A, B, C, and D. In which position mirror will be visible?
1. A, 2. B, 3. C, 4. D

Answer: 1. A
Explanation: In the case of A ray of light from A strikes a mirror and gets reflected back to make an angle of incidence and angle of reflection equal.

Question 5. A small hole P is made in a piece of cardboard. The hole is illuminated bya torch The pencil of light coming out of the hole falls on a mirror. At which point should the eye be placed so that the hole can be seen?
1. A, 2. B 3. C 4. D

Answer: 1. A
Explanation: The eye should be placed at position A because the hole can be seen only when the angle of incidence is equal to the angle of reflection.

Question 6. Two mirrors A and B are placed at right angles to each other

A ray of light incident on mirror A at an angle of 25° falls on mirror B after reflection. The angle of reflection for the ray reflected from mirror B would be
1. 25° 2. 50° 3. 65° 4. 115°
Answer: 3. 65°
Explanation: The angle of reflection for the ray reflected from mirror B will be 65° because the reflected ray from mirror A forms an incident ray on mirror 6 and is then reflected back by an angle of 65°;

Question 7. Which of the following statements is correct regarding rods and cones in the human eye?
1. Cones are sensitive to dim light.
2. Cones are sensitive to bright light.
3. Rods are sensitive to bright light.
4. Rods can sense color.
Answer: 2. Cones are sensitive to bright light.
Explanation: Cones are sensitive to bright light hence they sense color whereas rods are sensitive to dim light and they cannot sense color.

Question 8. In the figure of the human eye, the cornea is represented by the letter
1. A 2. B 3. C

Answer: 3. C
Explanation:
1. Iris
2. Lens
3. Cornea

Simplified Notes For KSEEB Class 8 Science Light 

Question 9. Name the part of the eye which gives color to the eyes
Answer: Iris the part of the eye which gives color to the eyes.

Question 10. Book while waving his hand very fast in front of his eyes, observes that his fingers for it?
Answer: The persistence of vision is the reason for their blurred vision Boojho while waving his hand very fast in front of his eyes, observes that his fingers appear blurred.

Question 11. How many times is a ray of light reflected by two plane mirrors placed parallel and facing each other?
Answer: An infinite number of times a ray of light is reflected by two plane mirrors placed parallel and facing each other.

Question 12. the angle between the incident ray and the reflected ray is 60°. What is the value of the angle of incidence?
Answer: 30°.
Explanation: The angle of reflection is equal to the angle of incidence. Since the Angle of incident ray + Angle of reflected ray is 60°.
The angle of incidence = 30°

Question 13. The distance between the object and its image formed by a plane mirror appears to be 24 cm. What is the distance between the mirror and the object?
Answer: The distance will be 12 cm
Explanation: Object + image formed =24 cm
Object + mirror =12 cm

Question 14. What happens to light when it gets dispersed? Give an example.
Answer: When the light gets dispersed it is split into its constituent colors. Ex: rainbow.

Question 15. showing the position of the plane mirror. Also, label the angle of incidence and angle of reflection on it.

Answer:

Question 16. Can the image of the child in it be obtained on a screen?

Answer: No, the image of the child cannot be obtained on a screen because the image is a virtual image.

Question 17. Eyes of the nocturnal birds have large cornea and a large pupils. How does this structure help them?
Answer: They can see objects even in faint light. As a large pupil and large cornea allow more light to enter their eyes.

Question 18. What kind of lens is there in our eyes? Where does it form the image of an object?
Answer: Our eyes have a convex type of lens and the image is formed on the retina.

Question 19. Which part of the eye gets affected if someone is suffering from cataracts? How is it treated?
Answer: If a person is suffering from cataracts their eye lens will be cloudy. Cataracts can be treated by replacing the opaque lens with an artificial lens.

Question 20. Boojho planned an activity to observe object A through pipes so that he could see objects which he could not directly see.

1. How many mirrors should he use to see the objects?
2. Indicate the positions of the mirrors in the figure.
3. What must be the angle with respect to the incident light at which he should place the mirrors?
4. Indicate the direction of the rays
5. If any of the mirrors are removed, will he ee be able to see the objects?

Answer:
1. Three mirrors should he use to see the SHOU AN ee Pio Anat objects.

Question 21. There is a mistake in each of the following directly see. ray diagrams given
Answer:

Question 22. Explain the process which enables us to perceive motion in a cartoon film.
Answer: Carton movie is actually a projection of a static picture. 24 pictures per second are shown in a specific order which gives us the perception of movement.

Question 23. How is the phenomenon of reflection used in making a kaleidoscope? What are the applications of a kaleidoscope?
Answer: The kaleidoscope gives a number of images formed by reflection from the mirrors inclined to one another. Designers and artists use kaleidoscopes to get ideas for new patterns to design wallpapers, Jewellery, and fabrics.

Question 24. The word REST wrote in two ways in front of a mirror. Show how the word would appear in the mirror.
Answer:

Karnataka State Board Syllabus for Class 8 Textbooks Solutions

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials: metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Conservation of Plants and Animals
• Chapter 7 Force and Pressure
• Chapter 8 Friction
• Chapter 9 Sound
• Chapter 10 Combustion and Flame
• Chapter 11 Cell Structure and Functions
• Chapter 12 Reproduction in Animals
• Chapter 13 Reaching the age of Adolescence
• Chapter 14 Chemical Effects of Electric Current
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water

KSEEB Solutions for Class 8 Science Chapter 17 Stars And The Solar System Points To Remember

Celestial Bodies: All natural bodies visible in the sky, outside the Earth’s atmosphere, constitute the celestial bodies, e.g. stars, planets, their moons, comets, asteroids, meteors, etc.
The Moon is the celestial body closest to us. Stars are celestial bodies that emit light of their own. Our sun is also a star.

It is convenient to express the distances of stars in light years. A light year is a distance covered by light in one year. Stars appear to move from east to west. The pole star appears to be stationary from the Earth because it is situated close to the direction of the axis of rotation of the Earth.

Solar system: The Sun and the celestial bodies that revolve around it form the solar system. It comprises a large number of bodies like planets (8 known to date), their moons, comets, asteroids, meteoroids, meteors, and meteorites. These objects are held together in the solar system due to Sun’s gravitational pull.

Sun: It is the source of almost all energy on Earth. It continuously emits huge amounts of heat and light.

Planets: Planets reflect sunlight that is incident on them. They have no light of their own, so they don’t wrinkle like the stars. Planets have definite paths called orbits in which they revolve around the sun.

The time taken by a planet to complete one full revolution around the sun is called it’s period of revolution. The time taken by a planet to rotate a full 360 degrees on its axis is called it’s period of rotation. The time taken by a planet to complete one revolution increases as the distance from the sun increases.

There are eight planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Venus is the brightest planet in the night sky. Jupiter is the largest planet of the solar system

Other members of our solar system are:
1. Asteroids: These are rocky planetary bits or- biting around the sun, asteroid belt lies between Mars and Jupiter.
2. Comets: These are celestial bodies that revolve around the sun. It appears generally as a bright head with a long tail. The tail of a comet is always directed away from the Sun. A comet is made up of rock, dust water, ice, and frozen gases.
3. Meteors and Meteorites: Meteoroids are chunks of rock or particles of debris in our solar system. They are smaller than comets. When meteoroids enter the Earth’s atmosphere they are called meteors. Most meteors burn up in the at atmosphere, but if they survive the frictional heating and strike the surface of the Earth they are called meteorites. As a meteor glows brightly when it falls to the ground it is called a shooting star.
4. Satellites A body revolving around another body is called a satellite. Moon is the natural satellite of the Earth. Some planets also have natural satellites.

Artificial Satellites: Man-made objects sent into space to orbit the earth, Example: IRS, EDUSAT, INSAR. The artificial satellites revolve around the Earth. They are much closer than the moon Artificial satellites are used for weather forecasting, long-distance communication, and remote sensing.

Stars are luminous bodies that appear as points of light in the night sky. Our Sun is also a star. Many of the stars that we see in the sky are much bigger than the sun. But as they are quite far away from us, they appear very small.

Constellations: A group of stars forming some kind of recognizable figures or patterns is known as a constellation. Constellations appear to move from east to west as Earth rotates from west to east, Orion- the Hunter, Ursa Major- the Great Bear or Saptarishi, and Cassiopeia are some constellations.

The Moon is the celestial body closest to us. It is the only natural satellite of the Earth. It is a non-luminous body and it reflects the sunlight incident on it. Due to its revolution around the Earth, when it is at different positions in its path, the apparent disc of the Moon changes, which gives rise to its phases.

Class 8 Science KSEEB Stars And The Solar System Notes 

Stars And The Solar System NCERT Textbook Exercises

Question 1. Which of the following is NOT a member of the solar system?
1. An asteroid
2. A constellation
3. A satellite
4. A comet

Answer: 2. A constellation

Question 2. Which of the following is NOT a planet of the sun?
1. Sirius
2. Mercury
3. Saturn
4. Earth

Answer: 1. Sirius

Question 3. Phases of the moon occur because
1. We can see only that part of the moon that reflects light toward us.
2. Our distance from the moon keeps changing.
3. The shadow of the Earth covers only a part of the moon’s surface.
4. The thickness of the moon’s atmosphere is not constant.

Answer: 1. We can see only that part of the moon that reflects light toward us.

Question 4. Fill in the blanks.
1. The planet which is farthest from the Sun is Neptune.
2. The planet which appears reddish in color is Mars.
3. A group of stars, which appear to form a pattern in the sky is known as a constellation.
4. A celestial body that revolves around a planet is known as a satellite.
5. Shooting stars are actually not stars.
6. Asteroids are found between the orbits of Mars and Jupiter.

Question 5. Mark the following statements as true (T) or false (F).
1. Pole star is a member of the solar system. ( )
2. Mercury is the smallest planet in the solar system. ( )
3. Uranus is the farthest planet in the solar system. ( )
4. INSAT is the artificial satellite. ( )
5. There are nine planets in the solar system. ( )
6. Constellation Orion can be seen only with a telescope. ( )

Answer: True/False

1. False
2.True
3. False
4.True
5. False
6. False

Question 6. Match items in column A with one or more items in column B.

Column  A                                               Column B
Inner planets                                           1. Saturn
Outer planets                                          2. Great Bear
Constellation                                           3. Moon
Satellite of the Earth                               4. Mars

Answer:
Column A                                                    Column B
Inner planets                                                4. Mars
Outer planets                                               1. Saturn
Constellation                                                2. Great Bear
Satellite of the Earth                                     3. Moon

Question 7. In which part of the sky can you find Venus if it is visible as an evening star?
Answer: Venus appears in the western sky just after sunset.

Question 8. Name the largest planet of the solar system.
Answer: Jupiter is the largest planet of the solar system.

Question 9. What is a constellation? Name any two constellations.
Answer: The stars forming a group that has a recognizable shape is called a constellation.

Question 10. Draw sketches to show the relative positions of prominent stars in
1. Ursa Major and
2. Orion.

Answer: 

Question 11. Name two objects other than planets that are members of the solar system.
Answer: Satellites and asteroids are objects that are members of the solar system.

Question 12. Explain how you can locate the Pole Star with the help of Ursa Major.
Answer: To locate the Pole Star we should look toward the northern part of the sky and identify UrsaMajor. We may look at the two stars at the end of Ursa Major. A straight line passing through these stars is imagined and is extended towards the north direction. This line leads to a star that is not too bright. This is the Pole Star.

Question 13. Do all the stars in the sky move? Explain.
Answer: No, no star moves in the sky. They appear to move from east to west because the Earth rotates from west to east about its axis.

Question 14. Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light years?
Answer: The distance of stars is so large that it cannot be expressed in terms of kilometers. That is why very large distances are expressed in another unit known as a light year. One light year is the distance traveled by light in one year. If the distance of a star is eight light years, it means that this distance is the distance traveled by light in one year.

Question 15. The radius of Jupiter is 11 times the radius of Earth. Calculate the ratio of the volumes of Jupiter and the earth. How many earths can Jupiter accommodate?
Answer: The radius of the Earth is r.Then, the radius of Jupiter is 11r. So, the ratio of the volumes of Jupiter and Earth

formula

So, the ratio of the voLumes of Jupiter and Earth is 1331:1
So, 133:1 Earth can accommodate Jupiter.

KSEEB Class 8 Science Solutions For Stars And The Solar System 

Question 16. Boojho made the following sketch of the solar system. Is the sketch correct? If not correct it.

Answer: No, the diagram made by Boojho is not correct, because in the solar system the sequence of the planets of their distance from the sun is like; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Here he had changed the positions of the planets Venus, Mars, Neptune, and Uranus. Besides this, he had shown in the diagram that shows the Asteroids belt in the gap between the orbits of Saturn and Jupiter. This is incorrect The Asteroids belt is located in the middle of the orbits of Jupiter and Mars.

Stars And The Solar System Activities

Question 1. Observe the moon continuously for several nights, preferably from one full moon to the next. Make a sketch of the moon every night in your notebook and note the day from the day the part of the sky (east or west) in which the moon is seen.

Answer: We find that there is a change in the shape of the moon every day and the moon appears to be perfectly round on a full moon day. On the fifteenth day of the month, we see that the moon is not visible even if the sky is clear. Thus, the moon goes on increasing every day, till on the fifteenth day and the full face of the moon the bright part of the moon goes on decreases every night and by another fifteen days again the new moon is formed.

Question 2. Draw a circle of about 1 m in diameter on the ground. Ask one of your friends to stand at the center of this circle. You revolve around your friend in such a manner that your face always remains towards him. Can your friend see your back? How many rotations did you complete in one revolution? The moon revolves around the Earth in a similar manner.
Answer: No, my friend cannot see my back. One rotation is completed in one revolution. It is concluded that the moon completes one rotation on its axis as it completes one revolution around the earth.

Question 3. Stand in the center of a big room and start rotating. In which direction will the objects in the room appear to move? Do you see them moving in the direction opposite to your motion?
Answer: The object appears to move in the opposite direction to our motion.

KSEEB Class 8 Science Solutions For Stars And The Solar System 

Question 4. Take an umbrella and open it. Make about 10-15 stars out of white paper. Paste one star at the position of the central rod of the
umbrella and others at different places on the cloth near the end of each spoke Now rotate the umbrella by holding its central rod in your hand. Observe the stars on the umbrella. Is there any star that does not appear to move? Where is this star located? If there were a star located where the axis of rotation of the Earth meets the sky, could this star also be stationary?

Answer: Yes, the star situated at the central rod of the umbrella does not appear to move. Star located at the axis of the earth meets the sky is also stationary. Thus, the Pole star situated in the direction of the earth’s axis does not appear to move.

Question 5. Observe this constellation (Ursa Major) for a few hours. Do you find any change in its shape? Do you find any change in its position?
Answer: It is observed that the shape of the constellation remains the same but the constellation appears to move in the sky from east to west.

Question 6. This activity should be performed on a clear moonless night during summer at about 9.00 p-m. Look towards the northern part of the sky and identify Ursa Major. You may get help from elders in your family. Look at the two stars at the end of Ursa Major. Imagine a straight line passing through these stars Extend this imaginary line towards the north direction. (About five times the distance between the two stars.) This line will lead to a star that is not too bright. This is the Pole star. Observe the Pole star for some time. Note that it does not move at all as other stars drift from east to west.

Answer: Pole star is a prominent star and is aligned with the Earth’s axis of rotation. So Pole star does not move at all with respect to other stars.

Question 7. During a summer night, observe Ursa Major 3-4 times at an interval of 2 to 3 hours. Also, locate the Pole star each time. Does Ursa Major appear to move from east to west? Does it appear to revolve around the Pole star? Compare your observations with those Ursa Major moves around the Pole star
Answer: It is concluded that all the stars of Ursa Major appear to revolve around the Pole star.

Question 8. Go out into the playground with four or five of your friends. Draw four circles of radii 1m, 1.8 m, 2.5 m, and 3.8 m, all having a common center Ask one of your friends to stand in the center and represent the Sun. Your other four friends may represent Mercury, Venus,
Earth and Mars. Ask your friends to move around the Sun in an anti-clockwise direction in their own orbits Do they collide with one another?

Answer: No, they do not collide with one another, because they have fixed orbits of their own. In a similar way, planets move in their own orbits.

Stars And The Solar System Additional Questions

Question 1. Name the planet nearest to the Sun.
Answer: Mercury

Question 2. What is the speed of light?
Answer: 300000 km per second (3 x 10° m/s).

Question 3. Which is the brightest planet in the night sky?
Answer: Venus

Question 4. Which planets do not have satellites of their own?
Answer: Venus and Mercury

Question 5. Why Earth appears blue from space?
Answer: Due to the presence of water Earth appears blue from space

Question 6. Which planet is the least dense among all?
Answer: Saturn

Question 7. Name the unit which is used to measure astronomical distances.
Answer: Lightyear

Question 8. What are meteors?
Answer: Meteors are bright streaks of light in the sky produced by the entry of small meteoroids into the Earth’s atmosphere. They are also called shooting stars.

Question 9. Define the phases of the Moon.
Answer: The various shapes of the bright part of the Moon as seen during the month are called phases of the Moon,

Question 10. What makes life possible on planet Earth?
Answer: Some special environmental conditions responsible for the existence and continuation of the life of the Earth are :
1. Right distance from the Sun
2. Right temperature range
3. Presence of water
4. Presence of oxygen and hostile atmosphere
5. Presence of blanket of ozone

Stars And The Solar System Class 8 KSEEB Questions And Answers 

Question 11. Differentiate between the following :
1. Star and planet
Answer:
Star
1. Star twinkles in the sky.
2. It has its own light.
3. It is fixed at a point.
4. It is very big in size.
Planet
1. Planet does not twinkle in the sky.
2. It has no light.
3. It revolves around the sun.
4. It is very small compared to.the.star.
2. Asteroid and comet
Asteroid
1. Asteroids are made up of metals and rocky materials.
2. It rotates nearer to the sun.
3. It does not has any tail of volatile material.
Comet
1. Comets are made up of ice, dust, and rocky material.
2. It rotates farther from the sun.
3. It has a tail of volatile gases when passing close to the sun.
3. Galaxy and Constellation
Answer:
Galaxy
1. It is a collection of billions of stars.
2. It does not resemble the shape of human beings or animals.
3. There are billions of galaxies in the Universe.
Constellation
1. It is a collection of only a few stars.
2. It is arranged in patterns resembling human beings or some animals.
3. There are only about 88 constellations.

Question 12. Explain why we see phases of the moon.
Answer: The moon does not have its own light. We see the moon because the sunlight falling on it gets reflected toward us. Thus, we see only that part of the moon that reflects light keeps on changing daily. This happens because the moon revolves around the earth along with this moon also revolves around the sun. Therefore, we see phases of the moon.

Stars And The Solar System Multiple Choice Questions

Question 1. Morning star is the name given to
1. Pole star
2. Star Sirius.
3. Planet Jupiter
4. Planet Venus

Answer: 4. Planet Venus.
Explanation: Planet Venus is dazzling than any other stars and it is visible in the eastern sky before sunrise.

Question 2. Sun appears to move from east to west around the earth. This means that earth rotates from
1. East to west
2. West to east
3. North to south
4. West to north

Answer:2. West to east
Explanation: Sun appears to move from east to west around the earth which means the earth is rotating in the opposite direction.

Question 3. An astronaut standing on the surface of the moon throws a ball upwards. The ball would
1. Directly fall down from the point it is released.
2. Hang in space.
3. Go up and then come back to the surface of the moon.
4. Keep going up never to come back.

Answer: 3. Go up and then come back to the surface of the moon.
Explanation: On the moon acceleration due to gravity is lesser than earth hence the ball will go up and then come back to the surface of the moon.

Question 4. Suppose a new planet is discovered between Uranus and Neptune. Its time period would be
1. Less than that of Neptune.
2. More than that of Neptune.
3. Equal to that of Neptune or Uranus.
4. Less than that of Uranus.

Answer: 1. Less than that of Neptune.
Explanation: We know that the time period is directly proportional to the distance from the sun. Hence a new planet discovered between Uranus and Neptune will have less time period than the Neptune and greater than the Uranus.

Question 5. The change in seasons on the earth occurs because
1. The distance between the earth and the sun is not constant.
2. The axis of rotation of the earth is parallel to the plane of its orbit.
3. The axis of rotation of the earth is perpendicular to the plane of its orbit.
4. The axis of rotation of the earth is tilted with respect to the plane of its orbit.

Answer: 4. The axis of rotation of the earth is tilted with respect to the plane of its orbit.
Explanation: Axis of rotation of the earth is not perpendicular to the plane of its orbit. The tilt is responsible for the change of seasons on earth.

Explanation Of Stars And The Solar System In KSEEB Science 

Question 6. Do stars emit light only during the night?
Answer: Stars emit light always, but cannot see them during the day because of the excessive brightness of the sun.

Question 7. Paheli and Boojho observed a bright object in the night sky that was not twinkling. Paheli says, it itis a star, and Boojho says it is a planet. Who is correct?
Answer: Boojho is right because only planets cannot twinkle whereas stars emit light from a far distance and they twinkle.

Question 8. State whether the following statements are ‘True’ or ‘False’.
1. The planet nearest to us is Jupiter.
2. All the stars are at the same distance from us.
3. The planets do not emit light of their own.
4. The planets keep changing their position with respect to stars.
5. The planet Venus appears in the eastern sky before sunrise.
6. The plane in which the earth revolves around the sun is called the equatorial plane of earth.

Answer:
1. False: Mars and venus are the nearest plans to earth
2. False: Different stars are at distance from us
3. True
4. True
5. True
6. False: Earth revolves around the sun in the orbital plane

Question 9. John saw the full moon on a particular day. After how many days will he be able to see the full moon again?
Answer: Approximately 29 days

Question 10. Astar is ten light-years away from the earth. Suppose it brightens up suddenly today. After how much time shall we see this change?
Answer: We will see the change after 10 years.

Question 11. Meteors are not visible during the daytime. Explain the reason.
Answer: Meteors are not visible during the daytime because the brightness of a meteor is extremely small compared to that of the sun.

Question 12. Why does the moon change its shape daily?
Answer: We see only that part of the moon from which the light of the sun is reflected toward us. Hence the moon changes its shape daily.

Question 13. Paheli saw the moon through a glass window at 8:00 p.m. She marked the position of the moon on the glass pane. She got up at 4 a.m. in the morning. Will the moon be visible in the same position?
Answer: No, Because the position of the moon keeps changing during the night.

Question 14. Suppose the moon emits light of its own. Would it still have phases? Justify your answer
Answer: The moon does not emit its own light and reflects the light of the sun. phases are seen. Because of the revolution of the earth, reflections of different intensities of light fall on the moon. Because of this moon glows continuously forming phases.

Question 15. Explain why we always see the same side of the moon.
Answer: We always see the same side of the moon because the moon’s period of revolution around the earth is equal to the period of rotation of the moon on its axis. Hence we can only the side that faces us.

Question 16. Suppose the distance between earth and sun becomes half of its present distance. What is likely to happen to live?
Answer: Life may no longer exist because some special environmental conditions are needed for the existence and continuation of life on the earth. The right distance of the earth from the Sun is necessary so that it has the right temperature range, the presence of water and a suitable atmosphere, and a blanket of ozone.
Flow Chart:

Karnataka State Board Syllabus for Class 8 Textbooks Solutions

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials: metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Conservation of Plants and Animals
• Chapter 7 Force and Pressure
• Chapter 8 Friction
• Chapter 9 Sound
• Chapter 10 Combustion and Flame
• Chapter 11 Cell Structure and Functions
• Chapter 12 Reproduction in Animals
• Chapter 13 Reaching the age of Adolescence
• Chapter 14 Chemical Effects of Electric Current
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water