Question

A 10mm long awl pin is placed vertically in front of a concave mirror.A 5mm long image of the awl pin is formed at 30cm in front of the mirror. the focal length of this mirror is

Answer 1

m = hi / ho

m = -10/5

m = -2

1/f = 1/v + 1/u

v/f = 1 + m

f = v / (1+m)

f = 30 / -1

f = -30 cm