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 33 - Electromagnetic Induction - Exercises and Problems - Page 998: 29

Answer

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Work Step by Step

We have here a loop and a changing flux, so we must have an induced current. We know that the induced current is given by $$I=\dfrac{\varepsilon}{R}\tag 1$$ where the induced emf $\varepsilon$ is given by $$\varepsilon=\left|\dfrac{d\Phi}{dt}\right|$$ where $\phi =AB\cos\theta$ and here $A$ is constant and $\theta= 0^\circ$, so that $$\varepsilon=A\left|\dfrac{dB}{dt}\right|$$ where $B$ is given by $B=4t-2t^2$; $$\varepsilon= A\left|\dfrac{d }{dt}(4t-2t^2)\right|$$ $$\varepsilon= L^2\left (4 -4t \right)\tag 2$$ where $L$ is the side length of the square. Plug $\varepsilon$ from (2) into (1), $$I=\dfrac{ L^2}{R} \left(4 -4t \right)$$ Plug the known; $$I=\dfrac{ 0.20^2}{0.10} \left(4 -4t \right)$$ $$I=1.6\left(1 -t \right)$$ At $t=0$ s, $$I=1.6\left(1 -0\right)$$ $$I=\color{red}{\bf 1.6}\;\rm A$$ At $t=1$ s, $$I=1.6\left(1 -1\right)$$ $$I=\color{red}{\bf 0}\;\rm A$$ At $t=2$ s, $$I=1.6\left(1 -2\right)$$ $$I=\color{red}{\bf -1.6}\;\rm A$$ The negative sign indicates an opposite direction of the current.
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