Fundamentals of Physics Extended (10th Edition)

Published by Wiley

Chapter 34 - Images - Problems - Page 1039: 20b

Answer

$f=+16cm$

Work Step by Step

Solve the lens equation $$\frac{1}{f}=\frac{1}{p}+\frac{1}{i}$$ for focal length $f$: $$\frac{1}{f}=\frac{i}{ip}+\frac{p}{ip}$$ $$\frac{1}{f}=\frac{i+p}{ip}$$ $$f=\frac{ip}{i+p}$$ Substitute known values of $i=+28cm$ and $p=+40cm$ yields a focal length of $$f=\frac{(+28cm)(+40cm)}{28cm+40cm}=+16cm$$

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