Question

Where must an object be placed in front of a convex lens of focal length 20cm to obtain a real and four times magnified image

Answer 1

Answer:

Object must be placed 30 cm in front of the mirror..

Explanation:

f = -20,

m = -v\u

-2 = -v/u, v = 2u

1/f = 1/v + 1/ u

[-1/20] = 1/2u + 1/u

u = - 30 cm.

Hope it will help you...!!

Answer 2

Explanation:

f = 20

m = 4

m = v/u

4 = v/u

v = 4u ..........(i)

1/f = 1/v - 1/u

1/20 = 1/4u - 1/u

u = -25 cm

From equation (i)

v = 4u

v = 4*-25

v = -100 cm

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