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Lesson on the power of a lens

Answer Text:
Power of lens
The power of a simple lens is given by the formula: Power = #1 / f#. The unit for power of a lens is diopter (D).
Example
Find the power of a concave lens of a focal length 25 cm.
Solution
Power =# 1 / f = 1 / -0.25# = -4D.