Physics - Geometrical Optics Question with Solution | TestHub

Focal length of the convex lens, $f_1=+40\text{ cm}=+0.4\text{ m}$

Power of the convex lens, $P_1=\frac{1}{f_1}=\frac{1}{0.4}=+2.5\text{ D}$

Focal length of the concave lens, $f_2=-25\text{ cm}=-0.25\text{ m}$

Power of the concave lens, $P_2=\frac{1}{f_2}=\frac{1}{-0.25}=-4.0\text{ D}$

Power of the combination, $P=P_1+P_2$

$P=+2.5\text{ D}-4.0\text{ D}=-1.5\text{ D}$

Answer: $-1.5\mathrm{D}$