1. Twinkling of stars is due to atmospheric ?

internal reflection of light by clouds.

scattering of light by dust particles

refraction of light by different layers of varying refractive indices

dispersion of light by water droplets

Answer: refraction of light by different layers of varying refractive indices

Explanation:

Twinkling of star is due to atmospheric refraction of starlight caused by the gradual change in refractive index of different air layers at different height, the apparent position of star keeps on changing.


2. The bluish colour of water in deep sea is due to ?

absorption of light by the sea

reflection of sky in water

the presence of algae and other plants found in water

scattering of light

Answer: scattering of light

Explanation:

The fine water molecules mainly scatter blue light due to its shorter wavelength.


3. The focal length of the eye lens increases when eye muscles ?

contract and lens becomes thinner

are relaxed and lens becomes thinner

are relaxed and lens becomes thicker

contract and lens becomes thicker

Answer: are relaxed and lens becomes thinner

Explanation:

Ciliary muscles modify the curvature of eye lens. When eye muscles are relaxed, eye lens becomes thinner thereby are relaxed, eye lens becomes thinner thereby increase in the focal length of eye lens.


4. The clear sky appears blue because ?

light of all other colours is scattered more than the violet and blue colour lights by the atmosphere.

ultraviolet radiations are absorbed in the atmosphere.

violet and blue lights get scattered more than lights of all other colours by the atmosphere.

blue light gets absorbed in the atmosphere.

Answer: violet and blue lights get scattered more than lights of all other colours by the atmosphere.

Explanation:

Violet and blue colour have shorter wavelength. So, they scattered more than lights of other colour by the molecules present in the atmosphere.


5. A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power ?

– 0.5 D

– 0.2 D

+ 0.5 D

+ 0.2 D

Answer: – 0.5 D

Explanation:

Person cannot see distant objects clearly. So he is suffering from myopia. The defect is corrected by using concave lens of power P =1/f =-0.5


6. At noon the sun appears white as ?

red colour is scattered the most

blue colour is scattered the most

light is least scattered

all the colours of the white light are scattered away

Answer: light is least scattered

Explanation:

At noon, the sun is at top and the light rays coming from the sun have to travel lens distance hence, all colours get scattered very less even blue and violet.


7. The danger signals installed at the top of tall buildings are red in colour. These can be easily seen from a distance because among all other colours, the red light ?

is scattered the least by smoke or fog

moves fastest in air

is absorbed the most by smoke or fog

is scattered the most by smoke or fog

Answer: is scattered the least by smoke or fog

Explanation:

Red colour has longer wavelength so least scattered by smoke or fog.


8. When light rays enter the eye, most of the refraction occurs at the ?

pupil

crystalline lens

outer surface of the cornea

iris

Answer: outer surface of the cornea

Explanation:

Most of the refraction for light rays entering the eye occurs at the outer surface of cornea which acts a primary lens converging in nature.


9. At noon, the Sun appears white as ?

all the colours of the white light are scattered away

light is least scattered

red colour is scattered the most

blue colour is scattered the most

Answer: light is least scattered

Explanation:


10. Cornea is a transparent spherical structure which ____ ?

Scatters light

Reflects light

Refracts light

None

Answer: None

Explanation: