Differential Equations and Linear Algebra (4th Edition)

Published by Pearson
ISBN 10: 0-32196-467-5
ISBN 13: 978-0-32196-467-0

Chapter 1 - First-Order Differential Equations - 1.7 Modeling Problems Using First-Order Linear Differential Equations - Problems - Page 70: 15

Answer

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Work Step by Step

Using RC Circuit we get: $$\frac{di}{dt}+\frac{R}{L}=\frac{R}{L}$$ The integrating factor is: $$I=e^{\int \frac{R}{L}dt}=e^{\frac{R}{L}t}$$ Multiplying by integrating factor: $$e^{\frac{R}{L}t}\frac{di}{dt}+e^{\frac{R}{L}t}\frac{R}{L}=e^{\frac{R}{L}t}\frac{R}{L}$$ $$e^{\frac{R}{L}t}\frac{di}{dt}+e^{\frac{R}{L}t}\frac{R}{L}=e^{\frac{R}{L}t}E_0\sin wt$$ $$\frac{d}{dt}(e^{\frac{R}{L}q})=e^{\frac{R}{L}t}\frac{E_0}{L}\sin wt$$ Integrating both sides: $$e^{\frac{R}{L}q}=c-\frac{E_0e^{\frac{R}{L}t}(Lw \cos (wt)-R \sin (wt))}{L^2w^2+R^2}$$ $$q=ce^{-\frac{R}{L}t-\frac{E_0}(Lw \cos (wt)-R \sin (wt))}{L^2w^2+R^2}$$ As $t \rightarrow \infty$, the transient part of the solution is $ce^{\frac{R}{L}t}$ and the steady-state solution is: $-\frac{E_0(Lw \cos (wt)-R \sin (wt))}{L^2w^2+R^2}$
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