Question

How far must object placed from .
a concave mirror o f=20 to
real
image of magnification
of 1/4​

Answer 1

Answer:

the image formed is real and the mirror given is concave

so, focal length, f = -20cm

and, magnification = -1/4

magnification = -v/u

so, -v/u = -1/4

that is , u = 4v

according to mirror formula,

1/v + 1/u = 1/f

substitute u = 4v and f = -20cm

then, 1/v + 1/4v = 1/-20

that is, 5/4v = -1/20

so, v = -25cm

u = 4v

so, u =-100cm

so object should be placed 100 cm or 1 m in front of the concave mirror