VARDAAN LEARNING INSTITUTE

1. A person needs a lens of power -4.5 D for correction of her vision. (a) What kind of defect in vision is she suffering from? (b) What is the focal length of the corrective lens? (c) What is the nature of the corrective lens?
2. Why do stars appear to twinkle while the planets do not? Explain based on the concept of extended sources vs point sources.
3. A student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor give to her? Draw ray diagram for the correction of this defect.
4. Explain the role of ciliary muscles in the power of accommodation. What happens to them when viewing distant vs near objects?
5. Describe the formation of a rainbow in the sky with the help of a diagram. What are the three essential conditions for observing it?
6. Why does the Sun appear reddish early in the morning? Will this phenomenon be observed by an observer on the Moon? Justify your answer.
7. Draw a ray diagram to show the refraction of light through a glass prism. Mark on it (a) the incident ray, (b) the emergent ray and (c) the angle of deviation. Explain why the emergent ray bends towards the base.
8. A person is able to see objects clearly only when these are lying at distances between 50 cm and 300 cm from his eye. (a) Identify the dual defect. (b) Calculate the power of lenses required for the bifocal spectacles to correct this.
9. State the cause of dispersion of white light by a glass prism. How can we recombine the spectrum to get white light again?
10. What is atmospheric refraction? Explain how it affects the apparent length of the day.

11. A person looking at a person wearing a shirt with a pattern of horizontal and vertical lines is able to see the vertical lines more distinctly than the horizontal ones. What is this defect due to? How is it corrected?
12. When white light enters a prism, which color of light deviates the most and which the least? If monochromatic light (e.g., Green) enters the prism, will it split into colors? Explain.
13. Why is the field of view of a human eye (two eyes) $180^\circ$ but with one eye it is only $150^\circ$? What is the advantage of having two eyes located on the front of our face?
14. Is it possible to see a rainbow at noon? Justify your answer.
15. A glass slab causes lateral displacement, whereas a glass prism causes angular dispersion. Explain why.
16. If the refractive index of the material of a prism is $\sqrt{2}$ and the angle of prism is $60^\circ$, find the angle of minimum deviation.
17. Why does a beam of light become visible when it enters a smoke-filled room through a small hole? Name the phenomenon.
18. Explain why the planets do not twinkle but stars do. If a star is viewed from the moon, will it twinkle?
19. Why is the colour of the clear sky blue? What would be the colour of the sky if the earth had no atmosphere?
20. Explain why a hypermetropic person prefers to remove his spectacles while looking at distant objects.

Case I: The human eye is like a camera. Its lens system forms an image on a light-sensitive screen called the retina. The eye adjusts its focal length to focus on objects at different distances.

21. Name the part of the eye which acts as a screen.
22. Which part of the eye controls the amount of light entering it?
23. What is the range of vision for a normal human eye?
24. What is the nature of the image formed on the retina?

Case II: A student focuses the image of a candle flame on a white screen using a convex lens. He noted down the position of the candle, screen, and the lens.
Position of candle = 12.0 cm
Position of convex lens = 50.0 cm
Position of screen = 88.0 cm

25. What is the focal length of the convex lens?
26. Where will the image be formed if he shifts the candle towards the lens at a position of 31.0 cm?
27. What will be the nature of the image formed if he further shifts the candle towards the lens?
28. Draw a ray diagram to show the formation of the image in case (iii) as said above.

Case III: Atmospheric refraction is the phenomenon of bending of light on passing through earth's atmosphere. It causes many optical phenomena.

29. Why do stars appear higher than they actual are?
30. Why is the sun visible 2 minutes before actual sunrise?
31. Does the apparent position of a star remain stationary? Explain.
32. Why don't planets twinkle?

Directions: Choose the correct option:

• (a) Both A and R are true and R is the correct explanation of A.
• (b) Both A and R are true but R is NOT the correct explanation of A.
• (c) A is true but R is false.
• (d) A is false but R is true.

33. Assertion: Red light travels faster in glass than violet light.
    Reason: Refractive index of glass is less for red light than for violet.
34. Assertion: A rainbow is always formed in the direction opposite to the sun.
    Reason: A rainbow is formed by the dispersion of sunlight by water droplets.
35. Assertion: The sky appears dark to passengers flying at very high altitudes.
    Reason: Scattering of light is not prominent at such heights due to thin atmosphere.
36. Assertion: Myopia is due to the excessive curvature of the eye lens.
    Reason: For a myopic eye, the image of a distant object is formed behind the retina.
37. Assertion: A prism bends light towards its base.
    Reason: Light travels faster in glass than in air.
38. Assertion: Danger signals are made of red light.
    Reason: The red light is scattered the most by smoke or fog.
39. Assertion: White light is dispersed into seven colors by a prism.
    Reason: Different colors of light bend through different angles with respect to the incident ray.
40. Assertion: A convex lens of suitable power is used for correcting hypermetropia.
    Reason: A convex lens converges the light rays.

Multiple Choice Questions:

41. The defect of vision in which a person cannot see the distant objects clearly but can see nearby objects distinctively is called: (a) Myopia (b) Hypermetropia (c) Presbyopia (d) Cataract
42. The splitting of white light into its component colors is called: (a) Refraction (b) Reflection (c) Dispersion (d) Scattering
43. Which of the following colors is scattered the least by fog, dust, or smoke? (a) Violet (b) Blue (c) Red (d) Yellow
44. The human eye forms the image of an object at its: (a) Cornea (b) Iris (c) Pupil (d) Retina
45. The amount of light entering the eye is controlled by: (a) Ciliary muscles (b) Pupil (c) Cornea (d) Iris