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

Options

A. 10cm
B. 15cm
C. -18.31cm
D. 20cm

Answer

C

Explanation

Distance of object from mirrorr
`=15+(33.25)/(4)xx3=39.93 cm`
Distance of image from mirrorr `=15+(25)/(4)xx3=33.75 `
For mirrorr , `(1)/(v)+(1)/(u)=(1)/(f)`
`=(1)/(-33.75)-(1)/(39.93)=(1)/(f)impliesf~~18.3cm.`