Question 293: Ray Optics

Question

Two thin lenses are of same focal lengths $(f)$, but one is convex and the other one is concave. When they are placed in contact with each other, the equivalent focal length of the combination will be :

Accepted Answer

$\frac{1}{f_{e q}}=\frac{1}{f_{1}}+\frac{1}{f_{2}}$
$\frac{1}{f_{e q}}=\frac{1}{f}-\frac{1}{f}$
$\mathrm{f}_{\mathrm{eq}}=\infty$

Answer

$f / 4$

Answer

$f / 2$

Answer

Infinite

Answer

Zero

Ray Optics

Two thin lenses are of same focal lengths (f), but one is convex and the other one is concave. When they are placed in contact with each other, the equivalent focal length of the combination will be :

Choose the correct answer: