If a lens can converge the sun rays at a point 20 cm away from its optical centre, the power of this

Question

If a lens can converge the sun rays at a point 20 cm away from its optical centre, the power of this lens is\

Professor PC Thomas Classes · Answer

(c) : Converging point, $f=20 \mathrm{~cm}$ Power $P=$ ?\ As we know that,\ Power of lens $=\frac{1}{	ext { focal length (inm) }} \Rightarrow P=\frac{1}{f(	ext { inm })}$\ $P=\frac{100}{20} \Rightarrow P=+5 \mathrm{D}$\ Hence, power of convex lens is +5 D .\