Question

A concave mirror produces a real image 1 cm tall of an object 2.5 mm tall placed 5 cm from the mirror. Find the position of the image and the focal length of the mirror.

Answer 1

h1 = -1cm

h2 = 2.5mm = 0.25cm

u = -5 cm

m = h1/h2 = -v/u

-1/0.25 = -v/ -5

-4 = v/5

v =-20

So, position of image = 20cm in front of mirror

now, using mirror formula , we get

1/f = 1/v + 1/u

1/f = 1/-20 + ( 1/ -5)

1/f = -1/20 + (-1/5)

1/f = -1 + (-4) / 20

1/f = -5/20 = -1/4

f = -4

focal length = -4 cm