A nearsighted person has a far point of 40cm. What power spectacle lens is needed if the lens is 2cm from the eye

The value is

Explanation:

From the question we are told that  

      The value of the far point is  

      The distance of the lens to the eye is  

Generally

Generally the power spectacle lens needed is mathematically represented as

Here is the object distance which for a near sighted person is

And   is the image distance which is evaluated as

=>    

=>    

So

=>      

=>