<prompt> The focal length of 0.25 m power of the lens is40 D4 D14 D25 D  <response>: It is measured as reciprocal of the focal length in metres i.e. P 1f . The unit of power is dioptre D. One dioptre is the power of a lens of focal length one metre.The focal length f of a lens is the distance between the optical centre and the principal focus.Power of a lens P is defined as the ability of the lens to converge a beam of light falling on the lens. 