VARDAAN LEARNING INSTITUTE

1. Draw a schematic diagram of the human eye and label the following parts: (a) Part that controls the amount of light entering the eye (b) Part where image is formed (c) Part that holds the lens in position.
2. Draw a ray diagram to show the formation of image in a myopic eye. Also show its correction using a suitable lens.
3. Draw a ray diagram to show the formation of image in a hypermetropic eye. Also show its correction.
4. Draw a ray diagram showing the dispersion of white light by a glass prism. Label the colors at the top and bottom of the spectrum.
5. Show the recombination of the spectrum of white light using two identical prisms.
6. Draw a diagram to explain the formation of a rainbow in the sky. Label the water droplet and sunlight.
7. Draw a diagram showing the refraction of light through a glass prism. Mark the angle of incidence, angle of emergence, and angle of deviation.
8. Using a diagram, explain why the sun is visible before actual sunrise.
9. Draw a diagram connecting the defects of vision (Myopia and Hypermetropia) with the change in focal length of the eye lens.
10. Illustrate with a diagram why stars appear higher in the sky than they actually are.

11. A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used? Calculate its power.
12. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.
13. A student has difficulty reading the blackboard while sitting in the last row. The doctor prescribes a lens of power -2.5 D. Find the focal length of the lens. Is he myopic or hypermetropic?
14. A person needs a lens of power -5.5 D for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 D. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?
15. The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?
16. Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.
17. A person can see clearly text of a book only when it is held at 40 cm from his eye. Calculate the power of the lens required to enable him to read at 25 cm.
18. Refractive index of glass is 1.5. Calculate the speed of light in glass. (Speed of light in vacuum = $3 \times 10^8$ m/s).
19. Light enters from air to glass plate having refractive index 1.50. What is the speed of light in glass? The speed of light in vacuum is $3 \times 10^8$ m/s.
20. A beam of light passes from air into a substance X. If the angle of incidence is $45^\circ$ and the angle of refraction is $30^\circ$, calculate the refractive index of substance X.
21. If the refractive index of water is 4/3 and that of glass is 3/2, find the refractive index of glass with respect to water.
22. A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.
23. Calculate the critical angle for a glass-air interface if the refractive index of glass is 1.5. ($\sin 42^\circ \approx 0.67$).
24. Two thin lenses of power +3.5 D and -2.5 D are placed in contact. Find the power and focal length of the lens combination.
25. A 5 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 30 cm. Find the position, nature and size of the image.

26. Why does the sky appear dark instead of blue to an astronaut?
27. Why does the Sun appear reddish early in the morning?
28. Why do stars twinkle but planets do not?
29. Why is the color of the clear sky blue?
30. Why are danger signal lights red in color?
31. Explain why the planets do not twinkle.
32. Why does the sun appear white at noon?
33. Why is a normal eye not able to see clearly the objects placed closer than 25 cm?
34. What happens to the image distance in the eye when we increase the distance of an object from the eye?
35. Why do we have two eyes instead of one?
36. Is the position of a star as seen by us its true position? Justify your answer.
37. Why do we see a rainbow in the sky only after rainfall?
38. Why is the red color selected for danger signals?
39. Why is the scattering of light responsible for the blue color of the sky?
40. Why do clouds appear white?

Case 1: A student is unable to see clearly the words written on the blackboard placed at a distance of approximately 3 m from him. Name the defect of vision the boy is suffering from. State the possible causes of this defect and explain the method of correcting it.

41. Identify the defect.
42. Suggest the corrective lens.
43. Draw the ray diagram for correction.

Case 2: When a beam of white light is passed through a glass prism, a band of seven colors is formed on a white screen. This phenomenon is called dispersion of light.

44. Which color bends the most and which bends the least?
45. What is the cause of dispersion?
46. Name a natural phenomenon based on this principle.

Practical Application:

47. A person is using spectacles with power -1.0 D. Is he suffering from myopia or hypermetropia? Can he focus on distant objects without glasses?
48. Why do old people often need two pairs of spectacles, one for reading and another for viewing distant objects? How is this problem resolved using a single pair?
49. During a foggy day, why do yellow fog lights help in driving?
50. Why does smoke coming from a fire often look blue?