Question

If the focal length of a concave lens is 25 cm, find the power of the lens.

Hint:

Remember: For concave lenses, the focal length is negative, and therefore the power is also negative.

Answer 1

The power P of a lens is related to its focal length f by the formula: P = (1)/(f) Where:
- P is the power of the lens in diopters (D),
- f is the focal length of the lens in meters.
Given that the focal length of the concave lens is 25 cm, we first convert it to meters: f = 25 cm = 0.25 m Now, applying the formula for power: P = (1)/(0.25) = -4 D The negative sign indicates that it is a concave lens.
Thus, the power of the concave lens is -4 diopters (D).