Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

Published by Pearson
ISBN 10: 0321740904
ISBN 13: 978-0-32174-090-8

Chapter 35 - AC Circuits - Exercises and Problems - Page 1053: 48

Answer

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Work Step by Step

$$\color{blue}{\bf [a]}$$ We know that the $\varepsilon_{\rm rms}=\varepsilon_0/\sqrt{2}$, so $$\varepsilon_0=\sqrt{2}\varepsilon_{\rm rms}=\sqrt{2}(120) $$ $$\varepsilon_0= \color{red}{\bf 170}\;\rm V$$ $$\color{blue}{\bf [b]}$$ The phase angle is given by $$\phi=\tan^{-1}\left[\dfrac{X_L-X_C}{R}\right]$$ where $X_L=\omega L=2\pi fL$, and $X_C=1/2\pi fC$ $$\phi=\tan^{-1}\left[\dfrac{2\pi fL-\dfrac{1}{2\pi fC}}{R}\right]$$ Plug the given; $$\phi=\tan^{-1}\left[\dfrac{2\pi (60)(0.15)-\dfrac{1}{2\pi (60)(30\times 10^{-6})}}{(100)}\right]$$ $$\phi=\color{red}{\bf -17.7}^\circ$$ $$\color{blue}{\bf [c]}$$ The average power loss is the power dissipated through the resistor which is given by $$P_R=I_{\rm rms}\varepsilon_{\rm rms}\cos\phi$$ where $I_{\rm rms}=\varepsilon_{\rm rms}/R$, $$P_R= \dfrac{\varepsilon^2_{\rm rms}\cos\phi}{R}$$ Plug the known; $$P_R= \dfrac{(120)^2\cos(-17.7^\circ)}{100}$$ $$P_R= \color{red}{\bf 137}\;\rm W$$
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