Question

(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.

Answer 1

(a) • Power of Accommodation: The ability of the human eye to adjust the focal length of its lens to focus on objects at varying distances.
• Part of the Eye: The ciliary muscles play a major role in the accommodation process.
• When the Eye Focuses on:
– (i) Nearby Objects: The ciliary muscles contract, making the lens more convex (thicker), which increases its refractive power to focus on nearby objects.
– (ii) Distant Objects: The ciliary muscles relax, making the lens less convex (thinner), which decreases its refractive power to focus on distant objects.

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(b).

Necessary Conditions to Observe a Rainbow:
• The Sun should be shining behind the observer.
• There must be water droplets in the air to refract, disperse, and reflect sunlight.