Question

A concave mirror has a magnification of -2.5 if its focal length is 20 cm find its image position?​

Answer 1

Explanation:

Magnification, h = -2.5

i.e. for a concave mirror

h = Size of image/ size of object

h = -v/u

hence, -v/u= -2.5

then, v = 2.5 u ------ (1)

According to mirror formula,

1/v + 1/u = 1/f ------ (2)

given focal length of concave mirror is 20

i.e. by Cartesian plane, f= -20 ----- (3)

Putting values of (1)&(3) in (2)

we get,

(1/2.5u)-1/u = 1/ -20

solving the equation we get u = -28 cm

By (1)

hence v= 2.5 x -28

v = -70 cm

Hence the position of image is 70 cm