Question 345: 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: