# A convex lens of diameter 8.0 cm

Question:

A convex lens of diameter $8.0 \mathrm{~cm}$ is used to focus a parallel beam of light of wavelength $620 \mathrm{~nm}$. If the light be focused at a distance of $20 \mathrm{~cm}$ from the lens, what would be the radius of the central bright spot formed?

Solution: