Power of a lens of focal length 25 cm is

The power of a lens (P) is defined as the reciprocal of its focal length (f) when measured in meters [1][2]. The standard unit for lens power is the dioptre (D), where 1 D = 1 m⁻¹. To calculate the power for a lens with a focal length of 25 cm, the value must first be converted to meters: 25 cm = 0.25 m. Applying the formula P = 1/f, we get P = 1 / 0.25, which equals +4 dioptres. In optics, a positive focal length indicates a convex (converging) lens, resulting in a positive power value. Therefore, a lens with a focal length of 25 cm has a power of +4 Dioptre.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > 9.3.8 Power of a Lens > p. 157
2. [2] https://en.wikipedia.org/wiki/Dioptre