Question

# I saw a question that a person is suffering from myopia and he has a far point of 80cm. In its solution it is mentioned that the object distance is infinity. How come it be?

Solution

## The far point of a normal eye is infinity. But, it shifts to a certain distance in a myopic eye. Hence, the image of an object at infinity needs to be formed at a point which is the far point of myopic eye. Hence the value of u is taken as infinity. ​​​​here is the solution,      As the defect is myopia so we need a diverging lens and the power of lens can be calculated as follows: v=-80cm,u=-infinity (bcoz the person can see to the specific distance which is as at infinfinty for him) we know that:1/f=1/v-1/u so substituting the values: 1/f=-1/80-(-1/infinity) 1/f=-1/80+0(1/infinity=0) 1/f=-1/80 therefore,f=-80cm or -0.8m now ,P=1/f P=-1/0.8 P=-1.25D

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