Q142 / 160 · AP EAMCET 2022 (07 Jul Shift 2) · Physics
An optician prescribes a corrective lens of power $+2 \mathrm{D}$, then the focal length of the required convex lens is
- A$10 \mathrm{~cm}$
- Correct answerB$50 \mathrm{~cm}$
- C$10 \mathrm{~m}$
- D$50 \mathrm{~m}$
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 $=50 \mathrm{~cm}$.
Hence, the correct answer is option: 'B'.