The equation relating the power of a lens to its focal length is:
power (in dioptres)=1focal length (in metres) \text{power (in dioptres)} = \frac{1}{\text{focal length (in metres)}} power (in dioptres)=focal length (in metres)1An optometrist prescribes a corrective lens with a power of 2.5 dioptres.
Calculate the focal length of this lens in cm.