Question

on of Light
Yard Stick
(First solve these questions yourself and then tally the answers by reversing next page)
2 cm high object is placed at a distance of 20 cm from a concave mirror. A real image is
Formed at 40 cm from the mirror. Calculate the focal length of the mirror. 13-33 (CB.SE.2011)​

Answer 1

Explanation:

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

here v= 40 (image is formed at the right side of the mirror) and u = 20

thus,

1/f = 1/20 + 1/40

f= 40/3 = 13.33 cm

and

m = v/u = hi/h0

hi = 40 × 2 / 20 = 4cm height