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A person can read the newspaper when it is held at 60 cm from his eyes. What should the focal length of his contact lenses be to allow him to read the newspaper comfortably at a distance of 30 cm? (A) -30 cm (B) 60 cm (C) -60 cm (D) 30 cm

Respuesta :

Answer:

Option B IS CORRECT.

Explanation:

The person suffers from long sighted-ness. The near point has gone far . For

an object kept at 30 cm to be visible, the image of it must be formed at 60 cm ie the ray of light must appear to be coming from 60 cm . for  it convex lens is required.  So

u = -30 cm

v = -60 cm

Using lens formula

1/v - 1/u = 1/f

- 1/ 60 + 1/ 30 = 1/f

( - 1 + 2) / 60 = 1 / f

f =  60 cm

Option B IS CORRECT.

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