The power of a converging lens is 4.5 D and that of a perging lens is 3 D. The power of this combination of lenses placed close together is :(a) +1.5D (b) +7.5D (c) −7.5D (d) −1.5D

Explanation

Given:

Power of the converging lens, $P_1$ = $+$4.5 D   (power of converging lens is always taken positive)

Power of the diverging lens, $P_2$ = $-$3 D    (power of diverging lens is always taken negative)

To find: Combined power of the two lenses, $P$.

Solution:

The power of the combination of lenses is given as-

$P=P_1+P_2$

Substituting the given value, we get-

$P=4.5D+(-3D)$