Respuesta :
The focal length of the lens is 40cm.
What is the focal length?
The distance between the center of a lens or curved mirror and its focus.
A plane convex lens is made of glass ( n = 1. 5) with one flat surface and the other having a radius of 20 cm.
The focal length of the lens is given by the following formula;
[tex]\rm \dfrac{1}{f}=(n-1) \left ( \dfrac{1}{r_1}-\dfrac{1}{r_2} \right)\\\\Where; \ r_1 =\infty , \ r_2=20, \ and \ n = 1.5[/tex]
Substitute all the values in the formula;
[tex]\rm \dfrac{1}{f}=(n-1) \left ( \dfrac{1}{r_1}-\dfrac{1}{r_2} \right)\\\\\rm \dfrac{1}{f}=(1.5-1) \left ( \dfrac{1}{\infty}-\dfrac{1}{20} \right)\\\\ \rm \dfrac{1}{f}=(0.5) \left ( 0-\dfrac{1}{20} \right)\\\\ \dfrac{1}{f} = \dfrac{-0.5}{20}\\\\\dfrac{1}{f}=-0.025\\\\f = \dfrac{-1}{0.025}\\\\f=-40[/tex]
Hence, the focal length of the lens is 40cm.
Learn more about focal length here;
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