(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.
(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.
(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.
