Question

A converging mirror has a focal length of 20 cm. Where should an object be placed so that its
virtual image will be twice as tall as the object?

Answer 1

given:

focal length

f= -20cm

and magnification

m = +2 = -v/u

or

v= -2u_______(1)

now, the mirror relation is

1/f = 1/v + 1/u

or

-1/20 = u + v/uv

= u-2u /-2u2 [substituting value of v from eq. (1)]

thus, image distance will be

u= -10cm

Answer 2

Hi..

1/d0 + 1/di = 1/f

And for the magnification to be 2 then di = 2do
Now substitute
1/do + 1/2do = 1/f
(2 +1)/2do = 1/f

3/2do = 1/f
2/3 * do = f
do = 3/2 f..



Hope this helps u!!