Question

Convex lens of focal length 15 cm is kept in series with a concave lens of focal length 30 cm. Find the power of the combination of lenses?

• A. 3.33 D
• B. + 0.033 D
• C. - 0.6 D
• D. + 0.6 D

Answer 1

The correct option is A

3.33 D

Given, focal length of convex lens $f_1=+15cm=0.15m$ and focal length of concave lens $f_2=-30cm=-0.30m$.

We know, Power of lens $P=\frac{1}{\text{focal length}}$

Power of convex lens $P_1=\frac{1}{0.15}$ and Power of concave lens $P_2=\frac{1}{-0.30}$

Total Power of combination ($P_{total}$) = $P_1$ + $P_2$

= $\frac{1}{0.15}$ - $\frac{1}{0.30}$

$P_{total}$ = 3.33 D

Therefore, the total power of combination is 3.33 D.