(a) Define the term power of accommodation of human eye. Write the name of the part of eye which plays a major role in the process of accommodation and explain what happens when human eye focuses (i) nearby objects and (ii) distant objects.

OR

(b) Draw a ray diagram to show the formation of a rainbow in the sky. On this diagram mark A - where dispersion of light occurs, B - where internal reflection of light occurs and C - where refraction of light occurs. List two necessary conditions to observe a rainbow.

Option (a)

1. Power of Accommodation: The ability of the eye lens to adjust its focal length is called accommodation.
2. Key Part: The ciliary muscles play a major role in modifying the curvature of the eye lens.
3. Focusing Mechanism:

• (i) Nearby objects: When looking at nearby objects, the ciliary muscles contract. This increases the curvature of the eye lens, making it thicker. Consequently, the focal length of the eye lens decreases, allowing nearby objects to be focused clearly on the retina.
• (ii) Distant objects: When looking at distant objects, the ciliary muscles relax. The lens becomes thin, and its focal length increases. This enables us to see distant objects clearly.

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Option (b)

1. Ray Diagram of Rainbow Formation:

• A: Point of entry where dispersion of light occurs.
• B: Point on the back inner surface where internal reflection occurs.
• C: Points of entry and exit where refraction occurs.

1. Two necessary conditions to observe a rainbow:

• (i) There must be water droplets present in the atmosphere (such as after a rain shower).
• (ii) The Sun must be behind the observer.