Question

what is the distance of a needle from a concave mirror of focal length 10cm for which a virtual image of twice its height is formed?

Answer 1

Explanation:

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Answer 2

answers

F = 10cm

height of image = 2 ( height of object )

h1 = 2 × h2 ____________(i)

-v/u = h1 / h2

-v/u = 2 × h2 / h2. ( from (i) )

-v/u = 2

-v = 2u

v = -2u _____________(ii)

1/v - 1/u = 1/f

1/-2u -1/u = 1/ f. ( from (ii) )

-1-2/ u = 1/f

-3/ u = 1/ 10

-3 × 10 = u

u = -30 cm

The distance of a needle from a concave mirror is -30 cm

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