Aperson 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

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.