Question

correct alternative and write the complete answer along with its letter of alphabet. 1 X 4 = 4

1. Power of a lens is -4, its focal length is

(a) 4m (b) -40cm (c) -0.25m (d) -25m

2. Disadvantage regarding solar energy is

(a) Eco-friendly (b) cells are expensive (c) Renewable (d) Used in rural areas

3.The human eye can focus objects at different distances by adjusting the focal length of the

eye lens,this is due to

(a) Presbyopia (b) accomodation (c) near sightedness (d) far sightedness

4.The coliform level in river Ganga at Devaprayag increased from 100 MNP/100ml

to 100000MNP/100 ml in 4 years.This indicates the water is

(a) potable (b) little contaminated (c) Highly contaminated (d) neutral

II. Answer the following questions: 1 X 4 = 4

5. Define refractive index

6.“Reuse is better than recycle” why?

7. Why does the sky appear dark to an astronaut?

8. Mention any two harmfull effects of nuclear energy.

III. Answer the following questions: 2X 5 = 10

9. Draw a ray diagram of image formed when an object is placed in front of convex lens between

f and 2f

10. How does mining cause pollution?

11. List four characteristics of the images formed by plane mirrors.

12. Why are we looking at alternative sources of energy?

13. The star proxima centauri twinkle but mars donot twinkle.why?

IV. Answer the following questions: 3X 5 = 15

14. Draw a labelled schematic diagram of biogas plant.

15. Explain the formation of rainbow in the sky with the help of a diagram.

16. Briefly explain three types of energies obtained from the sea?

17. What is wild life?How is wild life important for us?

18. Draw the diagrams to show (a) Hypermetropic eye (b) correction of that effect

V. Answer the following questions: 4X 3 = 12

19. Define power of lens.what is the S.I unit of power of a lens? If power of lens is +2p

what is the nature and focal length of the lens?

20. Describe the experiment to show how the refraction of light takes place through a glass prism.

21. The absolute refractive indices of glass and water are 4/3 and 3/2 respectively.If the speed of the

light in glass is 2X108 m/s.calculate the speed of light in (a) Vaccum(air) (b) water.

VI. Answer the following question: 5X 1 = 5

22.What is rain water harvesting? How can it be done at local level?What are its benefits?​

Answer 1

Ans . 22

Explanation:

Rainwater harvesting is a type of harvest in which the raindrops are collected and stored for future use, rather than allowing them to run off. Rainwater can be collected from rivers or roofs and redirected to a deep pit, aquifer, a reservoir with percolation, or collected from dew or fog with nets or other tools.

Answer 2

Answer:

Image formed by a plane mirror is always virtual and erect.

The size of the image is equal to that of the object.

The image formed is as far behind the mirror as the object is in front of it.

The image is laterally inverted.

Explanation: