Question

(a) 10 cm
(c) 20 cm
(b) 15 cm
(d) 30 cm
ir) is immersed in
A concave mirror gives an image three times as large as
the object placed at a distance of 20 cm from it. For the
image to be real, the focal length should be​

Answer 1

Answer:

a - 10 cm

Magnification (M) = h2/h1 [h2 = Height of image; h1 = Height of object]

M = -v/u [v = Image distance; u = Object distance]

u = -20 cm

Hence,

-3 = v/20

Or, v = -60 cm

By Mirror Formula, where f = focal length,

1/v + 1/u = 1/f

-1/60 -1/20 = 1/f

1/f = -1/60 -3/60

f = -15 cm

Answer = b - 15 cm