Question

It is intended to focus an image magnified 4 time using a converging mirror of focal length 20cm where should the object be placed.

Answer 1

Given m=4

m=-v/u

-v/u=4

v=-4u

also, f=-20

also, we know

1/v+1/u=1/f

1/4u+1/u=1/(-20)    (by applying all sign convention)

5/4u=-1/20

THERE FORE u=-25 cm

i hope it helped

Answer 2

Answer:

it is 2 times magnified, m = -2

so -v/u = -2

similarly, 1/v + 1/u = 1/f

so 1/v + 1/u = 1/-20

-v/v + -v/u = -v/-20 (multiply throughout by -v)

-1 -2 = v/20

-3 = v/20

v = -60

-2 = -v/u

-2 = 60/u

u = -30

so the object must be placed 30 cm from the mirror