CBSE Class 8

On this page, you will find NCERT Class 8 History Chapter 1 Notes Pdf free download. CBSE Class 8 Social Science Notes History Chapter 1 SST How, When and Where will seemingly, help them to revise the important concepts in less time.

How, When and Where Class 8 Notes Social Science History Chapter 1

CBSE Class 8 History Chapter 1 Notes Understanding the Lesson

1. History is/was always synonymous with dates.

2. Historians were always fascinated with dates.

3. History is about changes that occur over time.

4. History is about finding:

• How things were in the past.
• How things have changed.

5. Robert Clive asked Rennel to produce the maps of Hindustan.

6. Rennel saw maps preparation as essential to the process of domination.

7. A single date, cannot be fixed at which British rule was established, National Movement started or the changes took place within the economy and society gradually. All these happened over a stretch of time or a span of time.

8. Third son of Queen Victoria of Britain, Prince Arthur was given the title ‘Duke of Connaught’.

9. Dates in history are vital because that focuses on a particular set of events changes.

10. Histories written by British historians in India consider rule of each governor-general as important. These histories began with the rule of First Governor-General, Warren Hastings and ended with last Viceroy, Lord Mountbatten.

11. Warren Hastings became the first Governor-General of India in 1773.

12. History book narrates the deeds of governors-general, while biographies glorified them as persons and paintings protected them as powerful figures.

13. In 1817, James Mill (Scottish economist and political philosopher) published massive three volume work, A History of India’.

14. James divided History of India in three periods – Hindu, Muslim and British.

15. History is divided into different periods to capture the characteristics of a time, its central features.

16. Mill thought that Asian societies were at a lower level of civilization than Europe. According to him, before British rule in India, Hindus and Muslims despots ruled the country.

17. Mill felt there were religious intolerance, caste taboos and superstitions in India but after the British rule, Indian society became civilised.

18. Apart from the British classification, historians usually classified Indian History into:

• Ancient
• Medieval
• Modern

19. This periodization has been borrowed from west.

20. Modern in west is associated to growth of all forces of modernity that are – science, reason, democracy, liberty and equality.

21. Medieval describes society where features of Modem Society don’t exist.

22. Under the British rule, there was absence of equality, freedom or liberty. Therefore, some historians classified this period as colonial.

23. The subjugation of one country by another leads to change of political, economical and social condition. This process is referred to as colonisation.

24. Sources used by historians in their writings are:

• Official records of the British administration.
• Preserved letters and documents.
• Record rooms where records were preserved for administrative institutions.

25. Documents were copied carefully and beautifully written by the

26. By the middle of 19th century, there was spread of printing.

27. The National Archives of India came up in the 1920’s.

28. The practice of surveying became important under colonial administration.

29. The sources like diaries of people, accounts of pilgrims and travellers, autobiographies of important personalities, leaders and reformers were written to spread their ideas, these sources were produced by the literates. So this will not help anyone to understand how history was experienced and lived by the tribals, peasants, workers, etc.

How, When and Where Class 8 CBSE Notes Important Terms

Colonization: The subjugation of one country by the another leads to different kinds of changes in political, economical, social and cultural aspects. This process is referred to as colonization.

Calligraphists: These are people who are specialized in the art of beautiful writing.

Notes of History Class 8 Chapter 1 Time Period

1773: Warren Hastings became the First Governor-General of India.

1817: ‘A History of British India’ published by James Mill.

1857: Massive rebel against British rule broke out in 1857.

1920: The National Archives of India came up.

Class 8 Social Science Notes: Here we are providing CBSE Class 8 Social Science Notes PDF Chapter Wise free download of History, Geography, Civics, Economics. Students can get NCERT Notes for Class 8 Social Science and Important Points of Class 8 Social science Notes designed by subject expert teachers.

NCERT Class 8 Social Science Notes PDF

Here is the list of CBSE NCERT Class 8 Social Science SST Notes Chapter Wise based on the latest NCERT syllabus prescribed by CBSE.

NCERT Class 8 History Notes

Notes of Class 8 SST History: Our Pasts – III

1. How, When and Where Class 8 Notes
2. From Trade to Territory Class 8 Notes
3. Ruling the Countryside Class 8 Notes
4. Tribals, Dikus and the Vision of a Golden Age Class 8 Notes
5. When People Rebel Class 8 Notes
6. Colonialism and the City Class 8 Notes
7. Weavers, Iron Smelters and Factory Owners Class 8 Notes
8. Civilising the Native, Educating the Nation Class 8 Notes
9. Women, Caste and Reform Class 8 Notes
10. The Changing World of Visual Arts Class 8 Notes
11. The Making of the National Movement 1870s – 1947 Class 8 Notes
12. India After Independence Class 8 Notes

NCERT Class 8 Geography Notes

Notes of Class 8 SST Geography: Resources and Development

1. Resources Class 8 Notes
2. Land, Soil, Water, Natural Vegetation and Wildlife Resources Class 8 Notes
3. Mineral and Power Resources Class 8 Notes
4. Agriculture Class 8 Notes
5. Industries Class 8 Notes
6. Human Resource Class 8 Notes

NCERT Class 8 Civics Notes

Notes of Class 8 SST Civics: Social and Political Life – III

1. The Indian Constitution Class 8 Notes
2. Understanding Secularism Class 8 Notes
3. Why Do We Need a Parliament Class 8 Notes
4. Understanding Laws Class 8 Notes
5. Judiciary Class 8 Notes
6. Understanding Our Criminal Justice System Class 8 Notes
7. Understanding Marginalisation Class 8 Notes
8. Confronting Marginalisation Class 8 Notes
9. Public Facilities Class 8 Notes
10. Law and Social Justice Class 8 Notes

In this page, we are providing Pollution of Air and Water Class 8 Extra Questions and Answers Science Chapter 18 pdf download. NCERT Extra Questions for Class 8 Science Chapter 18 Pollution of Air and Water will help to score more marks in your CBSE Board Exams.

Class 8 Science Chapter 18 Extra Questions and Answers Pollution of Air and Water

Extra Questions for Class 8 Science Chapter 18 Pollution of Air and Water with Answers Solutions

Pollution of Air and Water Class 8 Extra Questions Very Short Answer Type

Question 1.
What is cause for starting of melting of Gangotri glacier?
Answer:
Global warming

Question 2.
Which health problem arises by air pollution?
Answer:
Respiratory problems like asthma, breathlessness, bronchitis, etc.

Question 3.
What is global warming?
Answer:
Increasing temperature in atmosphere.

Question 4.
Which gas is responsible for depletion of ozone layer?
Answer:
Chloroflurocarbons (CFC’s).

Question 5.
What does SPM stand for?
Answer:
Solid particulate matter.

Question 6.
What is the role of activated charcoal in purification of water?
Answer:
It removes finest particles suspended in water.

Question 7.
Name a greenhouse gas.
Answer:
Carbon dioxide, methane, water vapour (any one)

Question 8.
What is the formula of ozone?
Answer:
O₃

Question 9.
Name the agents that pollute air and water.
Answer:
Pollutants

Question 10.
Name the main air polluting gases.
Answer:
Sulphur dioxide, carbon monoxide and nitrogen oxides.

Question 11.
Which radiations are absorbed by CO₂?
Answer:
Infrared radiations

Question 12.
Define eutrophication.
Answer:
Enrichment of water bodies with nutrients like nitrates and phosphates is known as eutrophication.

Question 13.
Name one major source of water pollution.
Answer:
Untreated sewage

Question 14.
What is the function of ozone layer?
Answer:
Ozone layer protects us from ultraviolet rays of the sun.

Question 15.
Name diseases spread through drinking of contaminated water.
Answer:
Diarrhoea, typhoid, etc.

Question 16.
When was the Ganga action plan launched?
Answer:
In 1985

Question 17.
What is smog?
Answer:
The combination of smoke and fog is basically known as smog.

Pollution of Air and Water Class 8 Extra Questions Short Answer Type

Question 1.
What do you mean by water pollution?
Answer:
When water get contaminated by unwanted substances which have a harmful effect on both living and non-living things is referred to as water pollution.

Question 2.
What is the greenhouse effect?
Answer:
The reflected sun rays are trapped by the earth’s atmosphere. The trapped radiation warms the earth.
This process by which the temperature of the earth’s atmosphere rises is called greenhouse effect.

Question 3.
What are the main causes of air pollution?
Answer:
Following are the main causes of air pollution:

• Poisonous gases which are expelled by various industries.
• Gases emitted by vehicles.
• Smoke and dust which are arising day by day due to human activities.
• Smoke emitted by forest fire.

Question 4.
What do you mean by air pollution?
Answer:
When air is contaminated by unwanted substances which have a harmful effect on both living and non¬living things then it is referred as air pollution.

Question 5.
What are the factors that are responsible for water pollution?
Answer:
Water gets polluted when unwanted and harmful substances are added to the water. Discharging of untreated sewage into the river, leaching of chemicals from agricultural practices and industries, oil spills, etc., causes water pollution.

Question 6.
What are the harmful effects of global warming?
Answer:
Following are the harmful effects of global warming:

• It will increase the earth’s temperature.
• Increase in earth’s temperature may lead to rise in sea level due to melting of glaciers.
• Rise in sea level will flood the coastal and low-lying areas.
• Global warming may lead to extreme weather other than cold or heat extremes.
• It may also affect many flora and fauna which are sensitive to temperature and their extinction.

Question 7.
Which factors decides quality of potable water?
Answer:
Potable water is clear, tasteless, odourless, have no contaminants and right pH. It has no harmful minerals or their level is too low to affect human health.

Question 8.
What’is global warming?
Answer:
Carbon dioxide is increasing day by day and it is a warm gas, which increases the temperature of the earth’s atmosphere. It is called global warming.

Pollution of Air and Water Class 8 Extra Questions Long Answer Type

Question 1.
What do you mean by acid rain? How does it affect both living and non-living things?
Answer:
Due to fossil fuel and industrial combustions that mostly emits nitrogen oxides (NO_x) and sulphur dioxide (SO₂) into the atmosphere. Water vapour present in atmosphere reacts with these gases to form nitric acid and sulphuric acid. Normal rain water is slightly acidic with a pH range of 5.3-6.0, because carbon dioxide and water present in the air react together to form carbonic acid, which is a weak acid. When the pH level of rain water falls below this range due to combining with these acids in atmosphere, it becomes acid rain. Acid rain has significant effects on the world environment and public health.

Effect on aquatic environment: Acid rain lowers pH level below 5, most fish eggs cannot hatch. Lowering in pH can also kill adult fish.

Effect on forests: It makes trees vulnerable to disease, extreme weather, and insects by destroying their leaves, damaging the bark and arresting their growth.

Effect on soil: Acid rain highly impacts soil microbes and biological activity as well as soil chemical compositions. Thus affecting crop production.

Effect on architecture and buildings: Acid rain on buildings, especially those constructed with limestone, react with the minerals and corrode them away. This leaves the building weak and susceptible to decay. Irreplaceable damage can be caused to the old heritage buildings.

Effect on public health: When in atmosphere, sulphur dioxide and nitrogen oxide gases, degrades visibility and can cause accidents, leading to injuries and deaths. Intensified levels of acid depositions in dry form in the air can cause lung and heart problems such as bronchitis and asthma.

Other effects: Acid rain leads to weathering of buildings, corrosion of metals, and peeling of paints on surfaces. Acid rain also corrodes metals like steel, bronze, copper and iron.

Question 2.
What is eutrophication? How does it affect aquatic organisms?
Answer:
Enrichment of an ecosystem with nutrients, typically compounds containing nitrogen, phosphorous or both, is known as eutrophication. Eutrophication in lakes, ponds or rivers encourages the growth of algae and other aquatic plants. These algae grow rapidly in the water system and forms algal bloom. They compete for sunlight, oxygen and space. This badly affect the aquatic life and deteriorates water quality. This is also responsible for the large scale death of aquatic plants and animals.

Question 3.
Write a short note on water pollution.
Answer:
Water pollution is the contamination of water bodies (e.g., lakes, rivers, oceans, aquifers and groundwater). This form of environmental degradation occurs when pollutants are directly or indirectly discharged into water bodies without adequate treatment to remove harmful compounds.

Water is available both on surface and under the ground. The major pollutants of surface water are toxic and poisonous wastes from households, industries, nuclear wastes, oil spills, agricultural waste, accumulation of heavy metals, chemicals from chemical factories, microorganisms from human faeces, etc.

Groundwater is mainly contaminated by leaching of harmful chemicals into the soil. Seepage of sewer near groundwater aquifer contaminates with disease causing microorganisms. Accumulation of heavy metals in soil may also lead to groundwater pollution.

Water pollution affects the entire biosphere plants and organisms living in these bodies of water. In almost all cases the effect is damaging not only to individual species and population, but also to the natural biological communities.

Question 4.
How can you prevent water pollution?
Answer:

• Be careful about what you throw down your sink or toilet. Don’t throw paints, oils or other forms of litter down the drain.
• Use enyironment-friendly household products, such as washing powder, household cleaning agents and toiletries.
• Take great care not to overuse pesticides and fertilisers. This will prevent runoffs of the material into nearby water sources.
• By having more plants in your garden you are preventing fertiliser, pesticides and contaminated water from running off into nearby water sources.
• Don’t throw litter into rivers, lakes or oceans. Help to clean up any litter you see on beaches or in rivers and lakes, make sure it is safe to collect the litter and put it in a nearby dustbin.

Question 5.
How can you prevent air pollution?
Answer:

• Conserve energy-remember to turn off lights, computers, and electric appliances when not in use.
• Use energy efficient light bulbs and appliances.
• Limit driving by carpooling, using public transportation, biking and walking.
• Combine errands for fewer trips.
• Keep your automobile well-tuned and maintained. Follow the manufacturer’s instructions on routine maintenance, such as changing the oil and filters, and checking tyre pressure and wheel alignment.
• Choose environment-friendly appliances.
• Petrol can be substituted with CNG.
• Make fertilisers of biodegradable wastes instead of burning them.
• Plant more and more trees.
• Scrubbers need to be used in the smokestacks to reduce the amount of sulphur dioxide emission in air.

Question 6.
Name various techniques used for purification of water.
Answer:
Water which looks clean may still have disease carrying microorganisms and dissolved impurities. So, it is essential to purify water before drinking. Municipal bodies uses various physical and chemical processes before supplying water into households.

• Boiling: It is a very common practice use for obtaining safe drinking water. Boiling kills the germs present in the water.
• Filtration: This is a physical method of removing impurities and in some cases germs also. A popular household filter is a candle type filter.
• Chlorination is a commonly used chemical method for purifying water. It is done by adding chlorine tablets or bleaching powder to the water.
• Now-a-days filter with reverse osmosis (RO) which causes desalination of water along with activated charcoal (to filter impurities) and ultraviolet lamp (to kill microorganisms) are also used for purification of water.

Pollution of Air and Water Class 8 Extra Questions HOTS

Question 1.
Name any two sources which cause air pollution due to suspended particulate matter.
Answer:
Combustion of fuels and industrial activities.

Question 2.
Name three alternative sources of energy which do not cause any pollution.
Answer:
Wind energy, solar energy and hydropower.

Question 3.
The quality of air at various locations is monitored regularly by 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 and to take immediate action to control it causes.

Question 4.
What is the best way to dispose off dry leaves? Why?
Answer:
Dry leaves can be converted into compost which is good for maintaining soil nutrients. Secondly, it does not cause pollution.

Question 5.
We should plant trees and nurture the ones already present in the neighbourhood. Why?
Answer:
Plants absorb carbon dioxide gas and releases oxygen. Thus, they play important role in purifying the earth’s atmosphere. By absorbing CO₂ they also reduces the chance of global warming. Trees provide habitat to many birds and animals. They maintain water cycle in the nature and also prevent soil erosion.

Question 6.
Why is it advised that industries should switch over to cleaner fuels such as CNG and LPG in the Taj Mahal Zone in Agra?
Answer:
With mushrooming industries and oil refineries suspended particulate matter is increasing in the air. These suspended particulate matter, dust and dirt get settle on the marble giving the Taj Mahal a yellowish appearance. This is reducing the aesthetic value of one of the seven wonders of the world.

Pollution of Air and Water Class 8 Extra Questions Value Based (VBQs)

Question 1.
If we look at our daily routine, it will be observed that we use many chemicals which pollutes water bodies. But all these chemicals have become inseparable part of our daily life like detergents, toothpastes, soaps, shampoos, dish wash liquids and bars, disinfectants, etc. If this sewage from our house is discharged in water bodies untreated causes havoc.
(a) What is water pollution?
(b) What are the major pollutants of sewage from houses?
(c) Do you think we can do something in our end to reduce pollution from household?
(d) What values do we acquire from this?
Answer:
(a) Water pollution is the contamination of water bodies by directly or indirectly discharging pollutants without adequate treatment to remove harmful compounds.
(b) Grey water (from sinks, tubs, washing machines, etc.), soap, detergents, toilet paper, disinfectants, etc.
(c) Yes, we can minimise the use of many chemicals. We can use natural soaps, shampoos, toothpastes and detergents which are easy to decompose.
(d) Awareness that how day-to-day activities is also degrading the nature.

In this page, we are providing Stars and the Solar System Class 8 Extra Questions and Answers Science Chapter 17 pdf download. NCERT Extra Questions for Class 8 Science Chapter 17 Stars and the Solar System will help to score more marks in your CBSE Board Exams.

Class 8 Science Chapter 17 Extra Questions and Answers Stars and the Solar System

Extra Questions for Class 8 Science Chapter 17 Friction with Answers Solutions

Stars and the Solar System Class 8 Extra Questions Very Short Answer Type

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 10⁸ m/s).

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

Question 4.
Name the star which is nearest to our solar system.
Answer:
Alpha centuari

Question 5.
Which planets do not have satellite of their own?
Answer:
Venus and Mercury

Question 6.
How many planets are there in our solar system?
Answer:
Eight

Question 7.
Which planet is called Red planet?
Answer:
Mars

Question 8.
Why Earth appears blue from space?
Answer:
Due to presence of water Earth appears blue from space.

Question 9.
What is the other name of Orion?
Answer:
Hunter

Question 10.
Which planet is least dense among all?
Answer:
Saturn

Question 11.
Do stars emit light only during night time?
Answer:
No, they emit light all the time.

Question 12.
Name the unit which is used to measure astronomical distances?
Answer:
Light year

Question 13.
What is asteroid?
Answer:
Asteroid is a small rocky body orbiting the sun or found between the orbit of Mars or Jupiter.

Question 14.
Which is the other name of constellation Great Bear?
Answer:
Saptarishi

Question 15.
What is Sun?
Answer:
Sun is a star.

Stars and the Solar System Class 8 Extra Questions Short Answer Type

Question 1.
What are meteors?
Answer:
Meteors are bright streaks of light in the sky produced by the entry of a small meteoroids into the Earth’s atmosphere. They are also called the ‘shooting stars’.

Question 2.
What is a satellite?
Answer:
A satellite is defined as a heavenly body that moves around another heavenly body along its own orbit.

Question 3.
What is artificial satellite? Give examples.
Answer:
Satellites that are made by man are called artificial satellites. Example, INSAT, IRS EDUSAT, etc.

Question 4.
What are meteorites?
Answer:
The meteors which are so large that they do not evaporate completely before reaching the earth’s surface are called meteorites.

Question 5.
What are comets?
Answer:
Comets are the members of our solar system. They revolve around the sun in highly elliptical orbit as a bright head with a long tail.

Question 6.
Define phases of Moon.
Ans.
The various shapes of the bright part of the Moon as seen during the month are called phases of Moon.

Question 7.
What are celestial objects?
Answer:
The objects such as stars, the planets, the moon and many other objects, in the sky are called celestial objects.

Question 8.
What are planets?
Answer:
The celestial bodies which revolve around the sun are called planets. There are total eight planets in our solar system, namely, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

Question 9.
Why the Sun is also called as star?
Answer:
The Sun is also called as star because it has its own source of energy and it continuously emits light and heat.

Stars and the Solar System Class 8 Extra Questions Long Answer Type

Question 1.
What is the solar system? Explain.
Answer:
The sun along with the eight planets, the moons, and other heavenly bodies form the solar system. Our solar system is a part of the milky way galaxy. The sun is at the centre of the solar system around which all other planets rotate. Except Mercury and Venus, remaining six planets have their natural satellite revolving around them in a particular orbit. In our solar system, Earth is the only planet having life. This is due to the hostile conditions available in it. Sun is the ultimate source of energy for sustenance of life on the Earth.

Question 2.
What makes life possible on planet Earth?
Answer:
Some special environmental conditions responsible for the existence and continuation of life on the Earth are:

• Right distance from the Sun
• Right temperature range
• Presence of water
• Presence of oxygen and hostile atmosphere
• Presence of a blanket of ozone

Question 3.
Differentiate between the following:
(a) Star and planet
(b) Asteroid and comet
(c) Meteoroid and comet
(d) Galaxy and constellation
Answer:
(a) Star and planet

(b) Asteroid and comet

(c) Meteoroid and comet

(d) Galaxy and constellation

Question 4.
Write few lines about every planet of the solar system.
Answer:
There are total eight planets in our solar system which are as follows:

• Mercury: Mercury is the planet which is nearest to the sun. It is the smallest planet of the solar system. It has no satellite of its own.
• Venus: Venus is the second planet in our solar system. It is the brightest planet in the night sky.
  It has no moon or satellite of its own.
• Earth: It is the third planet of the solar system and is the only planet on which life exists. It has only one moon.
• Mars: The fourth planet of our solar system is Mars. It is also called the red planet. Mars has two satellites.
• Jupiter: It has large number of satellites and it is the largest planet of our solar system.
• Saturn: Saturn appears yellowish in colour. It contains beautiful rings which are not visible with naked eyes.
• Uranus: It is the seventh planet of our solar system. It is the second outermost planet of solar system.
• Neptune: It is the last planet of our solar system.

Question 5.
Explain why do we see phases of 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 which 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.

Question 6.
What is constellations? Name and explain some major constellations.
Answer:
The groups of stars that make an imaginary shape in the night sky are called constellations (nakshatras). They are usually named after mythological characters, people, animals and object they resemble in shape. There are 88 constellations known so far.

Some major constellations are:

• Ursa Major (Great Bear): It is one of the most well known constellations and the third largest one. It looks like a big dipper. It is visible in the northern hemisphere. It has groups of seven relatively bright star.
• Ursa Minor (Little Bear): It is ladle shape similar to Ursa Major. It also consists of seven stars. At the end of the Little Bear’s tail is the pole star. It is the nearest bright star to the north celestial Pole.
• Orion (Hunter): It has seven prominent stars. The three middle stars represent the belt of hunter and four stars form a quadrilateral.
• Cassiopeia: It is a constellation in the northern sky that looks like a distorted letter W or M. It is visible during the winter in the early hours of night.
• Leo: Leo contains several bright stars making it one of the most easily recognisable constellations in the night sky. It is visible in both Northern and Southern hemispheres.

Stars and the Solar System Class 8 Extra Questions HOTS

Question 1.
A star 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 shall see this change after ten years only because this change which occurred today will reach to our eyes through space after ten years only.

Question 2.
Why meteors are not visible during daytime?
Answer:
The brightness of the streak of light formed by meteors are extremely less compared to that of the sun. Thus, meteors are not visible during daytime.

Question 3.
If the moon emits light of its own, then would it still have phases?
Answer:
The moon does not have its own light. It shines due to the reflected light of the sun. Therefore, phases are formed. If the moon emits its own light then no shadows will be formed and hence as a result no phases will be formed.

Question 4.
Why do we always see the same side of moon?
Answer:
The period of rotation of the moon on its own axis is equal to the period of its revolution around the earth. So, we always see the same side of moon.

Question 5.
If the distance between Earth and Sun becomes half of its present distance, what is likely to happen to life? Justify your answer.
Answer:
If the distance between the Earth and the Sun becomes half, then temperature of Earth will increase to alarming levels. Water on the Earth will evaporate leaving it dry. Most of the plants will die. Thus, ultimately ending all the life on the Earth.

Stars and the Solar System Class 8 Extra Questions Value Based (VBQs)

Question 1.
Most people blame stars and planets in their horoscope for being unsuccessful in their lives. Rohan is one of them. He believes that positioning of Saturn in wrong place in his horoscope is the reason of his bad performance in studies.

(a) What are the heavenly bodies?
(b) Do you really think that these heavenly bodies play an important role in our failure or success?
(c) Have you ever heard these kind of things regarding your failure, success or before doing any auspicious work? From whom?
(d) What value of Rohan is shown here?
Answer:
(a) A natural celestial object, visible in the sky, such as a star, planet, natural satellite, asteroid, comet, moon or sun is known as heavenly body.
(b) No.
(c) Yes, I have often heard these kind of things from my grandparents, parents and priest.
(d) Rohan is very superstitious, lazy as rather than studying he is blaming planets, orthodox, etc.

In this page, we are providing Light Class 8 Extra Questions and Answers Science Chapter 16 pdf download. NCERT Extra Questions for Class 8 Science Chapter 16 Light will help to score more marks in your CBSE Board Exams.

Class 8 Science Chapter 16 Extra Questions and Answers Light

Extra Questions for Class 8 Science Chapter 16 Light with Answers Solutions

Light Class 8 Extra Questions Very Short Answer Type

Question 1.
Why fingers appear blurred when we move our hand very fast in front of our eyes?
Answer:
This is due to persistence of vision 1/16th of a second.

Question 2.
What makes things visible?
Answer:
When light reaches our eyes after striking an object, we are able to see an object.

Question 3.
Which element is used at the back of plane mirror?
Answer:
Silver

Question 4.
The distance between the object and its image formed by a plane mirror appears to be 18 cm. What is the distance between mirror and the object?
Answer:
9 cm

Question 5.
How is hypermetropia corrected?
Answer:
It is corrected by using convex lens.

Question 6.
How is myopia corrected?
Answer:
It is corrected by using concave lens.

Question 7.
A ray of light is incident on a mirror at an angle of 40°. What is the angle of reflection ?
Answer:
40°

Question 8.
Name a device which works on the principle of multiple reflection.
Answer:
Periscope

Question 9.
Can we see an object in the dark?
Answer:
No

Question 10.
What is the nature of the image formed by the plane mirror?
Answer:
Virtual and erect

Question 11.
Where is the image formed in a plane mirror?
Answer:
Behind the mirror

Question 12.
The angle between the incident ray and reflected ray is 100°. What is the value of angle of incidence?
Answer:

Question 13.
What is yellow spot?
Answer:
It is highly light sensitive spot for seeing things with highest clearness.

Question 14.
Give an example of night bird.
Answer:
Owl

Question 15.
What do we call the image that cannot be obtained on a screen?
Answer:
Virtual

Question 16.
Show mathematically, the first law of reflection.
Answer:
∠i = ∠r

Question 17.
Name the phenomenon shown in the figure.
Answer:
Lateral inversion.

Question 18.
Express the mathematical formula to calculate the number of images formed when two mirrors are inclined at θ angle. 360°
Answer:
Number of images

Question 19.
How many colours are there in a spectrum of white light?
Answer:
Seven

Question 20.
Name the scientist who studied that if a white light is passed through a prism, it splits into different colours.
Answer:
Sir Issac Newton

Question 21.
Name the spot inside the human eye where the image is not visible.
Answer:
Blind spot

Question 22.
Name the liquid found between the cornea and lens.
Answer:
Aqueous humour

Question 23.
Name the liquid found between the lens and the retina.
Answer:
Vitreous humour

Question 24.
Define the incident ray.
Answer:
The ray of light striking the surface is called an incident ray.

Question 25.
Define angle of reflection.
Answer:
The angle between the reflected ray and the normal is called the angle of reflection.

Light Class 8 Extra Questions Short Answer Type

Question 1.
Define light.
Answer:
Light is defined as a form of energy that stimulates sight and makes things visible.

Question 2.
What is reflection?
Answer:
The bouncing back of light into the same medium after it falls on a surface is called reflection.

Question 3.
What is a mirror?
Answer:
A piece of glass with a shiny metal-covered at back, that reflects light, producing an image of the object in front of it is known as mirror.

Question 4.
State the two laws of reflection.
Answer:
The two laws of reflection are:

• The angle of incidence is always equal to the angle of reflection.
• The incident ray, the reflected ray and normal all lie in the same plane.

Question 5.
How do we see various objects?
Answer:
We see various objects due to reflection. As we know all surface reflect light, when light falls on any object, it reflects the light. The reflected light reaches our eyes and we are able to see the object.

Question 6.
What do you mean by reflected ray?
Answer:
The ray of light which is returned back into the same medium after the incident ray strikes the surface ’ is called reflected ray.

Question 7.
What is irregular reflection?
Answer:
Irregular reflection is defined as the reflection of light from an uneven surface. In irregular reflection, the reflected beam is not parallel.

Question 8.
List the characteristics of an image formed in a plane mirror.
Answer:
The characteristics of an image formed in a plane mirror are:

• It is virtual.
• It is erect.
• It is of same size as the object.

Question 9.
What is lateral inversion?
Answer:
The phenomenon of changing left side to right and right side to left by the mirror while forming image is called lateral inversion.

Question 10.
What is the far point and near point of the human eye with normal vision?
Answer:
In optics, the farthest and closest point at which an object can be brought into focus by the eye are called far point and near point of the eye respectively. The far point of the human eye with normal vision is infinity. The near point of the human eye with normal vision is 25 cm.

Question 11.
What is aqueous humour?
Answer:
The space between the cornea and lens is filled with a liquid called the aqueous humour.

Question 12.
Differentiate between rod and cone cells.
Answer:
Rods are the rod-shaped cells present in the retina of an eye which are sensitive to dim light whereas cones are the cone-shaped cells present in the retina of the eye which are sensitive to bright light.

Light Class 8 Extra Questions Long Answer Type

Question 1.
Write a short note on Braille system.
Answer:
The most popular resource for visually challenged persons is Braille. Braille system was developed by Louis Braille. He himself was a visually challenged person. There is Braille code for common languages, mathematics and scientific notation. Many Indian languages can be read using the Braille system.

Braille system has 63 dot patterns or characters. Each character represents a letter, a combination of letters, a common word or a grammatical sign. Dots are arranged in cells of two vertical rows of three dots each. Patterns of dots to represent some English letters and some common words are shown in Fig. 16.26.

These patterns when embossed on Braille sheets help visually challenged persons to recognise words by touching. To make them easier to touch, the dots are raised slightly. Visually challenged people learn the Braille system by beginning with letters, then special characters and letter combinations. Methods depend upon recognition by touching. Each character has to be memorised. Braille texts can be produced by hand or by machine. Typewriter-like devices and printing machines have now been developed.

Question 2.
Explain the phenomenon of dispersion of light.
Answer:
Dispersion is defined as the phenomenon of splitting of white light into different colours on passing through a transparent medium such as prism. When white light is passed through a prism, it splits into seven colours. It is observed that the colours are in the following order:
Violet (V), Indigo (I), Blue (B), Green (G), Yellow (Y), Orange (O) and Red (R). The order of colours can be remembered by the acronym VIBGYOR. This coloured band is called spectrum of white light.

Question 3.
Write a note on ‘The Human Eye’
Answer:
Eye is a sense organ that enables us to see the world around us. It is roughly spherical in shape

• The first part that is bulged outward is called ‘cornea. It protects the eye.
• Behind the cornea, the coloured part of the eye, iris is present. It controls the size of the pupil.
• Pupil is a small opening in the cornea which allows the light to enter the eye.
• Behind the iris, eye lens is present which is a convex lens. It focus the image on retina, by bending the light rays.
• Retina is the inner back surface of the eye which acts as a screen to form image. It is sensitive to light.
• The sensation of the image formed on the retina is carried to the brain by the optic nerve.
• Optic nerve is connection between the eye and the

Question 4.
Write the ways to protect your eyes.
Answer:
Eyes are very delicate organ that enable us to see this colourful world. Thus, we must protect our eyes and take proper care of them.
Following are the ways to protect the eye:

• Always sit straight while reading or writing.
• Never read while walking or lying down.
• Wash your eyes frequently with clean water.
• Never read in the dim or too much bright light.
• Never rub your eyes with hands.
• Never bring the book too close to your eyes.
• Eat foods rich in vitamin A.

Question 5.
Explain some common eye defects in human.
Answer:
Some eye diseases are:
(i) Cataract: A cataract is a clouding of the lens in the eye leading to a decrease in vision. It can affect one or both eyes. Often it develops slowly. Symptoms may include faded colours, blurry vision, halos around light, trouble with bright lights, and trouble seeing at night. This may result in trouble driving, reading, or recognising faces. Cataracts are the cause of half of blindness and 33% of visual impairment worldwide. Cataract is treated by replacing the opaque lens with a new artificial lens.

(ii) Myopia: Near-sightedness or myopia, is the most common refractive error of the eye. Myopia occurs when the eyeball is too long, relative to the focusing power of the cornea and lens of the eye. This causes light rays to focus at a point in front of the retina, rather than directly on its surface. It can be corrected using spectacles made of concave lens.

(iii) Hypermetropia: Hypermetropia or long-sightedness occurs when eyeball is too short or the cornea or crystalline lens does not refract the light enough. This lead to formation of the image of a nearby object behind the retina. A hypermetropic person may have blurred vision when looking at objects close to them, and clearer vision when looking at objects in the distance. By placing a convex (plus powered) lens in front of a hypermetropic eye, the image is moved forward and focuses correctly on the retina.

(iv) Astigmatism: It is a defect in the eye or in a lens caused by a deviation from spherical curvature, which results in distorted images, as light rays are prevented from meeting at a common focus. It can be corrected by using a convex lens or concave lens or both.

Light Class 8 Extra Questions HOTS

Question 1.
What is power of accommodation?
Answer:
The process by which the ciliary muscles change the focal length of an eye lens to focus distant or near objects clearly on the retina is called power of accommodation.

Question 2.
How does large cornea and a large pupil in the eyes of the nocturnal birds help them?
Answer:
Large cornea and a large pupil allow more light to enter their eyes and they can see objects even in faint light.

Question 3.
What kind of lens is there in our eyes? Where does it form the image of an object?
Answer:
Convex lens is there in our eyes. It forms image of an object on the retina.

Question 4.
Boojho planned an activity to observe an object A through pipes A (Object to be seen) as shown in the given figure, so that he could see objects which he could not directly see.

(a) How many mirrors should he use to see the object?
(b) Indicate the positions of the mirrors in the figure.
(c) What must be the angle with respect to the incident light at which he should place the mirrors?
(d) Indicate the direction of rays in the figure.
(e) If any of the mirrors is removed, will he be able to see the object?

Answer:
(a) Three
(b)

(c) 45°
(d)

(e) No, he will not be able to see the object.

Light Class 8 Extra Questions Value Based (VBQs)

Question 1.
While playing, something entered into Somya’s eye. She immediately washed her eye with cold water. But as the irritation persisted, she immediately reported to her class teacher. Her class teacher took her to an eye doctor.

(a) What should be done if some foreign particles enter your eyes?
(b) Why is it not advised to rub your eyes when there is an eye irritation due to foreign particles?
(c) Do you think Somya was right in her action?
(d) What value of Somya is seen here?
Answer:
(a) We must do the following things:

• Restrict eye movement
• Shut the eyelid
• Do not rub eyes
• Try to clean it with splash of clear water
• Contact eye doctor immediately.

(b) Foreign object may cause abrasions or scratches on our cornea or rubbing. It may also cause bleeding of cornea.
(c) Yes.
(d) She is intelligent, knowledgeable and aware of such kind of small accidents.