A lens of power + 5 D has a focal length equal to
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 20 cm
The power of a lens in dioptres is the reciprocal of its focal length in metres.
\( \displaystyle f = \frac{1}{P} \)
\( \displaystyle f = \frac{1}{+5\,\mathrm{D}} = +0.2\,\mathrm{m} = 20\,\mathrm{cm} \)
The positive sign shows a converging (convex) lens.