Question

For combinations of two thin lenses are given in List I. The radius of curvature of all curved surfaces is r and the refractive index of all the lenses is 1.5. Match lens combinations in List I with their focal length in List II :

• A. P-1, Q-2, R-3, S-4
• B. P-2, Q-4, R-3, S-1
• C. P-4, Q-1, R-2, S-3
• D. P-2, Q-1, R-3, S-4

Answer 1

Answer: (B)

We use lens-makers' formula,
$\frac{1}{f_{eq}}=\frac{1}{f_1}+\frac{1}{f_2}$

Solving for a given set of lenses,we get

$A\to \frac{R}{2}$

$B\to R$

$C\to -R$

$d\to 2R$