Find the equivalent power of the thin lens combination shown in the figure. (1) +(R1 + R2 / R1 + R2)

Question

Find the equivalent power of the thin lens combination shown in the figure.

(1) \(+\left(\frac{R_1 + R_2}{R_1 + R_2}\right)\)

(2) \(- \left(\frac{R_1 + R_2}{R_1 R_2}\right)\)

(3) \( - \left(\frac{R_1+ R_2} {6R_1R_2}\right)\)

(4) \(+\left(\frac{R_1 + R_2}{6R_1R_2}\right)\) 

Answer 1

Correct option is : (3) \( - \left(\frac{R_1+ R_2} {6R_1R_2}\right)\) 

Net power = \(P_1 + P_2 + P_3\)

\( = - \frac{1}{6} \left( \frac{1}{R_1} + \frac{1}{R_2}\right)\) 

\( = -(\frac{R_1+ R_2}{6R_1R_2})\)