Question

A converging lens of focal length 50cm is placed coaxially in contact with another lens of unknown focal length. If the combination behaves like a diverging lens of focal length 50cm, find the power and nature of the second lens.

Answer 1

Dear Student

$$\begin{gathered} Powerofconverginglens{P}_1=\frac{1}{.5}=+2D \\ {P}_{total}=\frac{1}{-.5}=-2D \\ {P}_{total}=P_1+P_2 \\ -2=2+P_2 \\ {P}_2=-4D \\ so{f}_2=\frac{1}{P_2}=\frac{1}{-4}=-.25m=-25cm \\ Sonatureoflensisdivergingasfocallengthisinegative. \end{gathered}$$

Regards