Question

1.The far point of a myopic eye is 95 cm in front of the eye. What is the nature and power of the lens required to correct the problem?

2 . A person is able to see object's clearly when object's are placed between 55 cm and 250 cm from his eyes. (i) What kind of defect of vision he have? (ii) What kind of lenses he requires to overcome this defect?

answer fast please
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Answer 1

Answer:

Answer (1)

Power of lens = - 1 D

Nature of lens = Diverging

Answer (2)

(i) Myopia

(ii) Concave lens (diverging lens) of suitable power is required for correction of this defect.

Explanation:

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Explanation for (1)

position of object, u = - ∞

position of image, v = - 95 cm

Let, focal length of lens for correction = f

then,

Using Lens formula

→ 1/ f = 1/v - 1/u

(where f is the focal length of lens , u is the position of object and v is the position of image)

→ 1 / f = 1/(-95) - 1/(-∞)

→ 1/f = 1/(-95)

→ f = -95 cm

→ f = - 0.95 m

Now, Using formula for power of lens

→ P = 1 / f (in metres)

(where P is the power of lens and f is the focal length of lens in metres)

→ P = 1 / (-0.95)

→ P = - 1 D  (approx.)

so, Power of lens required for correction is -1 Dioptre and

Nature of lens will be diverging . (∵ lens power is negative).

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Explanation for (2)

(i)

The person is suffering from eye defect Myopia .

In this defect Far point of eye shifts towards the eye , and image is formed before retina not being on the retina .

A myopic person can see nearby objects clearly but cannot see distant objects distinctly.

Causes of Myopia defect are :

• Myopia defect arise due to Elongation of eyeball.
• This defect also arises by decrease in focal length of eye lens.

(ii)

Myopia defect could be overcome by using a diverging lens (Concave lens) of suitable power.

It will bring the image back on the retina.

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