The radius of curvature of a convex lens is $40 \mathrm{~cm}$, for each surface. Its refractive index is 1.5…
The radius of curvature of a convex lens is $40 \mathrm{~cm}$, for each surface. Its refractive index is 1.5 . Its focal length is
$40 \mathrm{~cm}$
$20 \mathrm{~cm}$
$80 \mathrm{~cm}$
$30 \mathrm{~cm}$
Solution
From the formula
$\begin{aligned} & \frac{1}{\mathrm{f}}=(\mu-1)\left(\frac{1}{\mathrm{R}_1}-\frac{1}{\mathrm{R}_2}\right) \\ & \frac{1}{\mathrm{f}}=(1.5-1)\left(\frac{2}{40}\right)=\frac{1}{40}\end{aligned}$
focal length, $f=40 \mathrm{~cm}$