Question

Frame a formula for the statement "the reciprocal of focal length $f$ is equal to the sum of reciprocals of the object distance $u$ and the image distance $v$".

Find $v$, when $f=15cm$ and $u=25cm$.

• A. $v=37.5$
• B. $v=33.2$
• C. $v=22.5$
• D. $v=33$

Answer 1

The correct option is A $v=37.5$

According to the qiestion, $\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$

Given, $f=15cm,u=25cm$

$\therefore \frac{1}{15}=\frac{1}{25}+\frac{1}{v}$

$\frac{1}{v}=\frac{1}{15}-\frac{1}{25}$

$=\frac{10-6}{150}$

$=\frac{4}{150}$

$\therefore v=37.5$