Question

the person wants to read a book placed at 20cm , whereas near point of his eye is 30cm . calculate the power of lens.

Answer 1

"From the given :  

The position of object from the observer is u=-20cm  

and

The position of object such that he can see v=-30cm  

To determine the power of the lens used p=?                            

The focal length of the lens is F= uv/(u-v)  

f= (-20)(-30)/((-20)-(-30))                                          

f=+60

Such that, the power of the lens must be given as p=100/f    

= 1.67D"