2022 · Q50
The magnitude of focal length of a concave lens is 2 m. What is the power of the lens?
general-sciencephysics-light-electricity
- A+0.5 dioptre
- B-0.5 dioptre
- C+2.0 dioptre
- D-1.0 dioptre
Explanation
The power P of a lens in dioptres is P = 1/f, where f is the focal length in metres. A concave (diverging) lens has a negative focal length, so f = −2 m and P = 1/(−2) = −0.5 dioptre. The positive options (A, C) would correspond to a convex lens, and option D miscalculates the reciprocal. Hence option B.