To find the focal length of a convex mirror , a student records the following data:
`{:("Object Pin","Convex Lens","Convex mirror","Image Pin"),(22.2 cm,32.2 cm,45.8 cm,71.2 cm):}`
The focal length of the convex lens is `f_(1)` and that of mirror is `f_(2)` . Then taking index correction to be negligibly small , `f_(1)` and `f_(2)` are close to :

Options

A. `f_(1)= 12.7 cm f_(2)= 7.8 cm`
B. `f_(1)= 7.8 cm f_(2)= 12.7 cm`
C. `f_(1)= 7.8 cm f_(2)= 25.4 cm`
D. `f_(1)= 15.6 cm f_(2)= 25.4cm`

Answer

B

Explanation

For convex lens

`u=-10cm`
`v=+39cm`
`f_(1)=(uv)/(u-v)=((-10)xx39)/(-10-39)=7.95cm`
For convex mirror

`R=25.4cm`
`f_(2)=12.7cm`