Question

A student focused the image of a candle flame on a white screen by placing the flame at various distance from a convex lens. He noted his observation as given below:

S.No	Distance of flame from the lens $\left(cm\right)$	Distance of screen from the lens $\left(cm\right)$
$1.$	$30$	$10$
$2.$	$20$	$12$
$3.$	$15$	$15$
$4.$	$12$	$20$

Find out the length of the given lens.

Answer 1

Then, $\frac{1}{V}=\frac{1}{15}-\frac{1}{15}=0$

or, $\frac{1}{\alpha }\Rightarrow V=\alpha$

but $V=70cm$ is given hence, observation.