(3)

The least distance of distinct vision for a young adult with normal vision is 25 cm. The range of vision of a normal human eye is from infinity to 25 cm.

(3)

The change in focal length of an eye lens is caused by the action of the ciliary muscles. The ciliary muscles help in changing the shape of the lens, thus changing its focal length.

(2)

The image formed on the retina of the human eye is real and inverted. Then in the retina, the image is converted into electrical impulses and sent to the brain. The brain flips that image into a virtual and erect image.

(2)

White light is dispersed into its seven-color components by a prism. Different colors of light bend through different angles with respect to the incident ray, as they pass through a prism. So, the Violet light refracts the most while passing through a prism.

(2)

A small opening in the iris is known as a pupil. Its size is controlled with the help of the iris. It controls the amount of light that enters the eye.

(2)

The cornea refracts light entering the eye from external objects. It is the transparent layer forming the front of the eye.

(2)

Least distance of distinct vision for a normal human being is 25 cm. It varies with age. For infants, it is 5 to 8 cm. The human eye can distinguish about 10 million colors.

(3)

Presbyopia occurs due to progressive weakness of the ciliary muscles and decreasing eye lens flexibility.

(2)

Myopia is a defect of vision in which a person clearly sees all the nearby objects, but is unable to see the distant objects.

(1)

In hypermetropia, the image is formed behind the retina and a person cannot see nearby objects clearly. It can be corrected by using a convex lens. It helps in focusing the rays entering the eye on the retina.

(1)

The scattering of light takes place due to the presence of particles in the atmosphere. This is because the atmospheric medium is very rare at higher altitudes, the scattering of light that takes place at these places is very low due to which the sky appears dark to the passengers flying at very high altitudes.

(3)

It is clear from the ray diagram that: The angle which is formed between the incident ray and the normal is called angle of incidence (p). The angle which is formed between emergent ray and the normal is called angle of emergence (y). The angle which is formed between the emergent ray and incident ray is called angle of deviation (z). Thus, angle of incidence, emergence and deviation is p, y and z respectively.

(1)

If a person is unable to read a newspaper, this means the person can’t see the nearby objects. Thus, he is suffering from hypermetropia and it can be treated by using a pair of convex lenses.

(2)

The persistence of vision of the human eye is 1/16 th of a second. Persistence of vision is the optical phenomenon where the illusion of motion is created because the brain interprets multiple still images as one.

(2)

The light-sensitive cell present on the retina and is sensitive to the intensity of light is rods.

(4)

The ciliary muscle also contracts and relaxes its longitudinal fibres to increase and decrease the size of the pore in the trabecular meshwork. The trabecular meshwork is responsible for aqueous humour drainage in the anterior portion of the eye.

 (1)

It is clear from the ray diagram that ∠A, ∠i and ∠D are correctly marked. ∠A represents the angle of prism which is correctly marked. ∠D represents the angle of deviation which is formed between the emergent ray and incident ray. ∠i is the angle formed by the incident ray with the normal. Thus, the correctly marked angles are ∠i, ∠A and ∠D.

(2)

The lens of power –0.5 D can be used to correct the defect as:
$F=-2m$
$P=1/f=1/(-2)=-0.5D$

(1)

A person with myopia can see nearby objects clearly but cannot see distant objects distinctly. Myopia is also known as short-sightedness.

(3)

The splitting of light into its constituent colours is called dispersion. It occurs because refraction or bending differs with the colour.

(3)

At noon, the sun is directly overhead and has lesser air to travel through, thus the distance to be travelled in air is reduced. Less scattering leads to the sun appearing white as only a little of the blue and violet colour is scattered.

(4)

Twinkling of stars is due to atmospheric refraction of starlight. The refraction of light occurs in a medium of various layers of gradually changing refractive indices. A star always emits light but the different layers of refractive indices in our atmosphere allow it to seem like a twinkle. When light enters the earth and hits the atmosphere from a distance, it begins to refract the light into any layer it reaches. Thus, the star appears to twinkle.

(4)

When white light enters a glass prism from air, the angle of deviation is least for red light. The white light consists of seven colours in which violet has the least wavelength and red colour has the maximum wavelength.

(4)

The white light consists of seven colours. Violet has the least wavelength, so its deviation is maximum. Red has the maximum wavelength, so its deviation is minimum.

(4)

Cataract is the medical condition in which the lens of the eyes becomes progressively opaque, resulting in blurred vision.