Question

Where should an object be placed in front of a concave mirror of focal length 20cm so as to obtain a two times magnified virtual image of the object

Answer 1

Explanation:

let u be the distance of object fro. the mirror.

f=20cm

m(magnification)=2

since m=-v/u

therefore

v=-2u

now putting values in formula

1/v + 1/u=1/f

-1/2u + 1/u=1/20

therefore

1/2u=1/20

1/u=1/10

u=10cm

i hope this is your soln. plzz mark it as brainliest

Answer 2

Since 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.