Power Of A Lens

Description:

Power of lens is the measurement of bending strength of a lens i.e. when a ray is incident on a lens then the degree with which the lens bends the ray is determined by the power of lens.

Power of lens is inversely proportionate to focal length i.e. greater will be the power of lens, greater will be the bending of ray and smaller will be the focal length as in the above figures, lens in figure 2 has more power as compared to the lens in figure 1.

P = 1/f

A lens which has focal length of 1 meter will have power equal to 1 diopter.

Power of convex lens is positive and power of concave lens is negative.

We have −

P = 1/f = (μ - 1)(1/R₁ - 1/R₂)

Observations

• Larger the value of refractive index, greater will be the Power of lens.

• For large power, radius is small and for small power, radius is large.

• For thick lens radius is small so power is large and for thin lens radius is large so power is small.