An optician prescribes a corrective lens of power $+2 \mathrm{D}$, then the focal length of the required…
An optician prescribes a corrective lens of power $+2 \mathrm{D}$, then the focal length of the required convex lens is
$10 \mathrm{~cm}$
$50 \mathrm{~cm}$
$10 \mathrm{~m}$
$50 \mathrm{~m}$
Solution
Power of a lens in diopters, $P=\frac{100}{f}$ $f=$ Focal length of lens in $\mathrm{cm}$. here,
$
P=+20 \mathrm{D}
$
so,
$
2=\frac{100}{f(\mathrm{~cm})} \Rightarrow f(\mathrm{~cm})=\frac{100}{2}=50
$
$\therefore$ Focal length of lens $=50 \mathrm{~cm}$