Question

At what distance from a concave mirror of focal length 10 cm should an object 2 cm long be placed in order to get an erect image 6 cm tall ?

Answer 1

Given that focal length,
f= -10cm

Magnification,
m= Image height/ Object height
= 6/2 = 3

Also magnification= - v/u

3= -v/u

v= -3u

As 1/u + 1/v = 1/f

1/u + 1/-3u = 1/ -10

Therefore u= -6.667

So object should be placed at a distance of 6.667 cm in front of the mirror.