The Human Eye and the Colourful World — Class 10 Science PYQs

(A) / Ciliary muscles of your eye contract and the eye lens become thick (1 Mark)

(A) / Iris and pupil (1 Mark)

(a)
* If the distance of the object from the eye is increased, ciliary muscles relax, lens becomes thin and so the focal length increases (1 Mark)
* If the distance between the object from the eye is decreased, the ciliary muscles contract, lens becomes thick and so the focal length decreases. (1 Mark)
OR
(b) In myopic eye image is formed in front of the retina. A concave lens / diverging lens of suitable power will bring the image back on to the retina. (2 Marks)

(i) While looking at objects nearer to eye, the curvature of the eye lens increases. Consequently, the focal length of the eye lens decreases. (1 Mark)
(ii) From 25cm (near point) to infinity (far point) (1 Mark)

(C)/ Presbyopia and hypermetropia.

(C) / Presbyopia (1 Mark)

(A) / converging lens (1 Mark)

(a)
* If the distance of the object from the eye is increased, ciliary muscles relax, lens becomes thin and so the focal length increases (1 Mark)
* If the distance between the object from the eye is decreased, the ciliary muscles contract, lens becomes thick and so the focal length decreases. (1 Mark)
OR
(b) In myopic eye image is formed in front of the retina. A concave lens / diverging lens of suitable power will bring the image back on to the retina. (2 Marks)

(B) / Red, Yellow, Green, Blue, Violet (1 Mark)

(D)/Angle between the directions of incident ray and emergent ray. (1 Mark)

(a) • Dispersion of light (1 Mark)
• Different colours of light bend through different angle with respect to incident ray as they pass through prism. (1 Mark)

Rainbow is caused by dispersion of sunlight by tiny water droplets, present in the atmosphere. The water droplets act like small prisms. They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrop.

(a) (i) Mainly blue coloured light is scattered because very fine particles scatter shorter wavelength.
(1)
(ii) Scattered light may appear white because very large size particles scatter light of all wavelengths.
(1)

Red colour is least scattered by fog or smoke, so it can be seen in the same colour from a large distance. (1 Mark)

* The phenomenon of spreading light in different directions on interaction with particles of the medium. (1 Mark)
* Light bounces back in a fixed direction after reflection while in scattering of light, it spreads in different directions. /Reflection of light is independent of the size of reflecting particles whereas the colour of the scattered light depends upon the size of scattering particles (2 Marks)

(a) • When a beam of light strikes fine particles like smoke, tiny water droplets, suspended particles of dust and molecules of air, the path of beam becomes visible. This phenomenon of scattering of light by colloidal particles is called Tyndall effect. (1 Mark)
• Examples: -
➤ When sunlight passes through a canopy of a dense forest tiny water droplets in the mist scatter light. (1 Mark)
➤ When a fine beam of sunlight enters a smoke-filled room through a small hole, scattering of light makes the particles visible.
(Any one, any other suitable example)
(b) (i) Blue light / light of shorter wavelength is visible. (½ Mark)
(ii) Red light/ Light of longer wavelength is visible. (½ Mark)