If the focal length of a convex lens is 50cm, which one of the following is its power?

The power of a lens is defined as the reciprocal of its focal length when measured in meters. The standard formula is P = 1/f (in meters), and the SI unit for power is the dioptre (D). For the given problem, the focal length of the convex lens is 50 cm. To calculate the power, this must first be converted to meters: 50 cm = 0.5 meters. Applying the formula, P = 1 / 0.5, which equals +2 dioptres. In optics, convex lenses are converging lenses and are conventionally assigned a positive focal length and positive power. Conversely, concave lenses have negative power. Therefore, a convex lens with a 50 cm focal length has a power of +2 dioptre.