Answer - 1 : - The ability of the lens of the eye to adjust its focal length to clearly focus rays coming from distant as well from a near objects on the retina, is known as the power of accommodation of the eye.

Question - 2 : - A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of corrective lens used to restore proper vision?

Answer - 2 : - An individual with a myopic eye should use a concave lens of focal length 1.2 m so that he or she can restore proper vision.

Question - 3 : - What is the far point and near point of the human eye with normal vision?

Answer - 3 : -

The minimum distance of the object from the eye, which can be seen distinctly without strain is called the near point of the eye. For a normal person’s eye, this distance is 25 cm.

The far point of the eye is the maximum distance to which the eye can see objects clearly. The far point of a normal person’s eye is infinity.

Question - 4 : - A student has difficulty reading the blackboard while sitting in the last row.

Answer - 4 : -

What could be the defect the child is suffering from? How can it be corrected?

Answer

The student is suffering from short-sightedness or myopia. Myopia can be corrected by the use of concave or diverging lens of an appropriate power.

Question - 5 : - The human eye can focus objects at different distances by adjusting the focal length of the eye lens. This is due to

Answer - 5 : -

(a) presbyopia (b) accommodation

(c) near-sightedness (d) far-sightedness

Answer-

(b) accommodation

Due to accommodation the human eye can focus objects at different distances by adjusting the focal length of the eye lens.

Question - 6 : - The human eye forms an image of an object at its

Answer - 6 : -

(a) cornea (b) iris

(c) pupil (d) retina

Answer –

(d) retina

The retina is the layer of nerve cells lining the back wall inside the eye. This layer senses light and sends signals to the brain so you can see.

Question - 7 : - The least distance of distinct vision for a young adult with normal vision is about

Answer - 7 : -

(a) 25 m (b) 2.5 cm

(c) 25 cm (d) 2.5 m

Answer –

25 cm is the least distance of distinct vision for a young adult with normal vision.

Question - 8 : - The change in focal length of an eye lens is caused by the action of the

Answer - 8 : -

(a) pupil (b) retina

(c) ciliary muscles (d) iris

Answer-

The action of the ciliary muscles changes the focal length of an eye lens

Question - 9 : - A person needs a lens of power -5.5 dioptres for correcting his distant vision.

Answer - 9 : -

For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?

Answer-

The power (P) of a lens of focal length f is given by the relation

Power (P) = 1/f

(i) Power of the lens (used for correcting distant vision) = – 5.5 D

Focal length of the lens (f) = 1/Pf= 1/-5.5 = -0.181 m

The focal length of the lens (for correcting distant vision) is – 0.181 m.

(ii) Power of the lens (used for correcting near vision) = +1.5 D

Focal length of the required lens (f) = 1/P

f = 1/1.5 = +0.667 m

The focal length of the lens (for correcting near vision) is 0.667 m.

Question - 10 : - The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?

Answer - 10 : -

The individual is suffering from myopia. In this defect, the image is formed in front of the retina. Therefore, a concave lens is used to correct this defect of vision.

Object distance (u) = infinity = ∞

Image distance (v) = – 80 cm

Focal length = f

According to the lens formula,

A concave lens of power – 1.25 D is required by the individual to correct his defect.

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