Far point of a myopic person is 40 cm. What type of lens should he wear so as to see the distant objects clearly? Calculate the focal length and the power of the lens he should use.
u =(infinity), v = - 40 cm, f = ?
Using the lens formula, we have
= 1/v-1/u =1/-40- 1/infinity = 1/-40 = 40 cm= -0.4 m
Hence, power of lens to be used is
P= 1/f = 1/-0.4 = -2.5D