A biconvex lens is used to project a slide on screen. The slide is `2 cm` high and placed at `10 cm` from the lens. The image is `18 cm` high. What is the focal length of the lens?

Options

A. `9 cm`
B. `18 cm`
C. `4.5 cm`
D. `20 cm`

Answer

A

Explanation

`(1)/(10)=(1)=(1)/(v)-(1)/((-15))`
`impliesv=+30 cm`
for small object `|dv|=(v^(2))/(u^(2))|du|`
`=((30)/(15))^(2)xx1=4 mm`