Q36E - University Physics with Modern Physics

Question

A lensmaker wants to make a magnifying glass from glass that has an index of refraction n = 1.55 and a focal length of 20.0 cm. If the two surfaces of the lens are to have equal radii, what should that radius be?

Step-by-Step Solution

Answer

The required radius is 22 cm with different sign.

Step 1: Determine the required radius

Use the Lensmaker’s equation

                        

Substitute the given values into the equation

                                           

                       

We want the term positive, to make it positive, ${\mathrm{R}}_2$must be negative and ${\mathrm{R}}_1$is positive

 

                      

Therefore, if the two surfaces of the lens are to have equal radii, the radii should be 22 cm and 22 cm.