A container is filled with water `(mu=1.33)` upto a height of 33.25cm. A convex mirror I s placed 15cm above the water level and image of an object placed at the bottom is formed 25cm below the water level. Focal length of the mirror is

Options

A. 10 cm
B. 15 cm
C. 20 cm
D. 25 cm

Answer

C

Explanation

Distance of object from mirror = `15 + (33.25)/(1.33) = 40 cm`
Distance of image from mirror = `15 + (25)/(1.33) = 33.8 cm`
For the mirror , `(1)/(v) + (1)/(u) = (1)/(f)`
`therefore (1)/(-33.8) + (1)/(-40) = (1)/(f) therefore f = -18.3 cm`
`therefore` Most suitable answer is (c)