Question

Calculate the distance between an object and its 3 times magnified real image formed by a concave mirror of focal length 21 cm.

Answer 1

f= 21cm

m= -3 (for real image )

m= v/-u

-3=v/-u

3u=v------(1)

1/21=1/v-1/(-u)

replacing u with v

-v/3=-u

1/21=1/v+3/v

4/v=1/21

v=84cm

now for u

1/21= 1/84 -1/(-u)

1/u=1/21-1/84

1/u=4-1/84

u=84/3

u=28cm

now for dist b/t image and object

u+v= 84+ 28 cm

= 112cm