Question

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

Answer 1

Answer:

Given that -

F = - 10 cm

O = 2 cm

I = 6 cm

V = ?

1 / F = 1 / V + 1 / U

1 / -10 = 1 / V + 1 / U

1 / -10 = ( U + V ) / VU

VU = -10 U - 10 V -----) 1 eqn

by magnification formula ,

M = - V / U = I / O

- V / U = 6 / 2

- V = 3 U

V = - 3U ---------) 2 eqn

put the value of V in eqn 1

U x - 3 U = - 10 u - 10 x - 3u

- 3U ^2 = - 10 U + 30 U = 20 U

- 3 U x U = 20 U

- 3 U = 20

U = - 20 / 3 = -6.66 cm

put the value of U in eqn 2

V = - 3U = -3 x - 6.66 = 19.98 cm