If focal length of a concave lens is \( 50\,\mathrm{cm} \), then the power of the lens would be
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( -2\,\mathrm{D} \)
The power of a lens is the reciprocal of its focal length in metres. A concave lens has a negative focal length (Cartesian sign convention).
\( \displaystyle f = -50\,\mathrm{cm} = -0.50\,\mathrm{m} \)
\( \displaystyle P = \frac{1}{f} = \frac{1}{-0.50} = -2\,\mathrm{D} \)