Question

A doctor has prescribed a corrective lens of power, −1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?

Answer 1

Power of a lens is given by:

Power (P) = $\frac{1}{\mathrm{f}}$

$f=\frac{1}{p}$
$\Rightarrow f=\frac{1}{-1.5}$

∴​ f = -66.67 cm.

Since the power is negative, the lens is of a diverging nature. Therefore, it's a concave lens.