Physics: Principles with Applications (7th Edition)

Published by Pearson
ISBN 10: 0-32162-592-7
ISBN 13: 978-0-32162-592-2

Chapter 21 - Electromagnetic Induction and Faraday's Law - General Problems - Page 623: 84

Answer

$5.8\times10^{-2}\;\rm A$

Work Step by Step

We know that the induced current is given by $$I=\dfrac{\varepsilon}{R}\tag 1$$ And we know that the induced $\varepsilon=\rm emf$ is given by $$\varepsilon= \dfrac{N_{coil}\Delta \Phi}{\Delta t}= \dfrac{N_{coil}\Delta (BA)}{\Delta t}$$ and we know that the cross-sectional area of the solenoid is constant, so $$\varepsilon= \dfrac{N_{coil}A_{solenoid}\Delta B_{solenoid}}{\Delta t}\tag 2$$ We also know that the magnetic field of the solenoid is given by $$B_{solenoid}=\dfrac{\mu_0N_{solenoid} I_{solenoid}}{l_{solenoid}}$$ Thus, $$\Delta B_{solenoid}=\dfrac{\mu_0N_{solenoid}\Delta I_{solenoid}}{l_{solenoid}}$$ Because $I$ here is the changeable one and all the other variables are constant. Plugging into (2); we will replace the titles of the coil by $c$ and the solenoid by $s$. $$\varepsilon= \dfrac{N_{c}A_{s} }{\Delta t} \cdot\dfrac{\mu_0N_{s}\Delta I_{s}}{l_{s}}= \dfrac{\mu_0N_{s}N_{c}A_{s} }{l_{s}\Delta t}\Delta I_{s}$$ Plugging into (1); $$I= \dfrac{\mu_0N_{c}A_{s} }{R\Delta t}\cdot \dfrac{N_{s}}{l_{s}} \cdot \Delta I_{s}$$ Plugging the known; $$I= \dfrac{4\pi \times10^{-7}\cdot 190 \cdot\pi (4.5\times10^{-2} )^2 }{12\cdot 0.10}\cdot \dfrac{230}{10^{-2}}\cdot (2-0)$$ $$I=\color{red}{\bf 5.8\times10^{-2}}\;\rm A$$ And its direction is to the east inside the resistor since the induced current is facing the sudden increase of the field.
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