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Give reason for the following:
1) Red light is used for danger signal
2) Cause of Color blindness.
3) Sky appears black in Moon.
4) Rainbow is seen on a rainy day in the presence of sunlight.
4) A person with a myopia eye cannot see objects beyond a distance of 1.5m. What would be the

power of corrective lens? Which type of lens is used?

5) What do you understand by myopia? Write two causes of it?

6) What do you mean by far point and near point of eye?

7) What is presbyopia? State the cause of it and how is it corrected?

8) Explain: 1) why does sky look blue on a clear day

2) Twinkling of stars.

9) What is hypermetropia? State two causes of hypermetropia with help of ray diagrams show:

1) The eye defect hyperopia.

1.Why does it takes sometimes to see in a dim room when you enter the room from bright sunlight outside?

ANS: In the bright iris causes the pupil to become smaller so that only a small portion of light enter the eye and rods of the retina are also adjusted in the same way. but when a person enter in to dim light each iris takes sometimes to increase the diameter of the pupil so that more amount of light can enter the eyes to see the objects clearly and rods of the retina also takes some time to adjust –themselves to get the picture of the object in the dim light.
2Can we see a rainbow on the moon?

ANS:No, since there is no atmosphere on the moon.

3.Does a beam of light give a spectum on passing through a hollow prism?

ANS:No,this is because dispersion of light cannot occur through a hollow prism containing air.



  1. Name the place where image is formed in the eye?

  2. Name the muscular diaphragm that controls the size of the pupil.

  3. What is the cause of dispersion of light?

  4. Give the cause of cataract of eye.

  5. Which color has got more wavelength?

  6. What makes bees respond to ultraviolet light?

1) What is the focal length of a plane mirror?

2) Which of the two has a great power, a lens of shot focal lenth or a lens of large length?

3) What does m= +1 stand for?

4) What is the power of a lens if its focal lenth is 50cm?

5) What is the nature of image at retina?

6) Name the point inside the lens through which a ray of light goes deviated?

7) What is the S.I. unit of power of a lens?

Home Assignment
1. Name the photographic film equivalent to our eye .

2.Why does a glass slab not disperse white light?

3.Why do we not perceive the depth of a lake ?

4.Name two causes of Myopia, Hypermetropia and presbiopia.

5.Name the liquids that keep our eye soft.

6.What causes rainbow formation?

7.What is Mirage?

Project work:

  1. To understand the dispersion of light with help of activity?

(Hint: materials, an irregularly shaped glass, white screen).

  1. List, observe, reason and explain three cases of nature where dispersion happens.

(hint: 1) Sun rise and sun set 2.Formation of rainbow.3.Twinkling of stars)

  1. Draw a labeled diagram of human eye and explain the function of retina, cornea, pupil, rods, and cones?

seminar: (students will be divided into groups 7 they will present papers on the topic)

  1. Means to overcome and Corrective measure

Topic 7: Management of natural resources


  1. Natural resources: it is stock of the nature such as air, water, soil, minerals, coal, petroleum, forest and wildlife that are useful to mankind in many ways.

  2. Pollution: it is defined as the undesirable change in physical, chemical or biological characteristics of our soil, air or water, which harmfully affect human lives or the lives of other species.

  3. pH of water: pH stands for ‘potential of hydrogen’. The acidic and basic character of aqueous solutions can be described in terms of hydrogen ion and hydroxyl ion concentration a pH below 7 indicates an acid solution and above 7 indicates an alkaline solution.

  4. Three R’s to save the Environment: We can reduce pressure on the environment by applying the maxim to ‘Reduce, Recycle and Reuse’ in our lives.

  5. Sustainable Development: It is the development which can be maintained for a long time without undue damage to the environment.

  6. Need to manage our Resources: Our natural resources are limited. With the rapid increase in human population, due to improvement in health care, the demand for all resources is also increasing.

  7. Biodiversity: It is the existence of a wide variety of species of plants, animals and microorganisms in a natural habitats with in a particular environment or of genetic variation with a species.

  8. Wildlife: It means all those naturally occurring animals, plants and their species which are not cultivated, domesticated and tamed.

  9. Water harvesting: It means capturing rainwater where it falls or capturing the run off in a local area and taking measures to keep the water clean by not allowing polluting activities to take place.

  10. Fossil Fuels: These fuels are obtained from the remains of plants and animals, which got buried beneath the earth millions of years ago, changed into coal, petroleum and natural gas due to excessive heat and high pressure inside the earth.

  11. Coal: It contains chiefly carbon and its compounds mainly nitrogen, oxygen, sulphur and hydrogen. It also contains inorganic matter.

  12. Non-renewable Energy Sources: These are energy sources which cannot be replaced easily when they get exhausted and are also called conventional sources of energy. E.g.: Fossil fuels.

  13. Uses of Fossil Fuels:

Coal: Thermal power plants and steam engines

Petroleum: Petroleum products like petrol and diesel are used as means of transport.

  1. Management of Fossil fuels: The natural gas is a good alternative to fossil fuels like coal and petroleum. The use of alternative source of non- conventional source of energy such as solar energy, wind energy, biomass energy etc. Should be promoted to save the reserves of fossil fuels .biogas can also be used for various purposes.


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