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A person stands 20cm in front of a concave makeup mirror and his upright image is twice as tall as his actual height. What is the focal distance of the mirror? a) 13cm b) 20cm c) 40cm d)10cm

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Answer:

c) 40 cm.

Explanation:

Since the image is upright , it must be virtual. Therefore image distance will be positive . object distance will be negative.

v/u = 2

u =- 20 cm

v = 40 cm

Using mirror formula

1/v + 1/u = 1/f

1/40 -1/20 = 1/f

(1-2)/40 = 1/f

f = - 40 cm.

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