Question

Two converging lenses with focal lengths f and 2f are positioned at a distance 3f apart. A parallel beam of light is incident on the lens with focal length f. If d is the incident beam width, what is the width of the emerging beam?

• A. $\frac{d}{2}$
• B. d
• C. 2d
• D. 4d

Answer 1

The correct option is B d

$\begin{array}{c}\text{parallel beam of width d strike the lens}{L}_1\text{,}\\ \text{it converges at}f\text{, Then it is focus of lens}L\text{.}\\ \text{The ray again becomes parallel to principal axis}\\ \text{with same width}d\text{.}\\ \therefore \text{correct option is (B)}\end{array}$