a doctor has prescribed a corrective lens of power -1.2 To a person suffering from myopia.

1) identify the defect from which he is suffering

2) Find the focal length of the lens

3. is the prescribed lens converging or diverging? show the nature of lens with diagram

Power of lens, P=1/f
Given,
Power, P=-1.2 D
Focal length, f=-0.833 m or -83.3 cm
Here, the power of lens is negative, so the corrective lens is a concave/diverging lens and the person is suffering from myopia.
The purpose of a concave lens for a myopic eye is to diverge the light from a far away object and make it appear nearer to the eye as shown in the diagram below.


 

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1. the person is suffering from short sightedness i.e.,a person clearly sees all the nearby objects, but is unable to see the distant objects comfortably and his eye is known as a myopic eye.A myopic eye has its far point nearer than infinity. It forms the image of a distant object in front of its retina.

2. P = -1.2 D , f = ?

P = 1

f(m)

f = 1

P

= 1

-1.2

= 0.83m

= 83cm

3. the prescibed lens is a diverging lens.

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