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 31 - Fundamentals of Circuits - Exercises and Problems - Page 918: 61

Answer

\begin{array}{|c|c|c|} \hline R&I({\;\rm A})& \Delta V ({\;\rm V})\\ \hline 4\;\Omega & \frac{9}{16}=0.56& 2.25 \\ \hline 12\;\Omega & \frac{3}{16}=0.19& 2.25 \\ \hline 5\;\Omega & \frac{3}{4}=0.75& 3.75\\ \hline 24\;\Omega & \frac{1}{4}=0.25& 6\\ \hline 3\;\Omega & 1& 3\\ \hline \end{array}

Work Step by Step

Let's assume that the current comes out from the 12-V battery and charging the 3-V battery, as you see in the last circuit below. Applying Kirchhoff's loop law on the last circuit below (d), starting from the left lower corner and moving clockwise. $$\Delta V_{\rm loop}=12-6I-3-3I=0$$ Hence, $$I=\bf1.0\;\rm A$$ This is the current that passes through $3\;\Omega$. From circuit (c), $$I=I_1+I_2=1\;\rm A\tag 1$$ where $$8I_1=24I_2$$ Hence, $$ I_1=3I_2$$ Plug into (1), $$1=3I_2+I_2 $$ Hence, $$I_2=\bf 0.25\;\rm A$$and $$I_1=\bf 0.75\;\rm A$$ From circuit (a), we can see that $I_1$ passes through $5\;\Omega$. Now we need to find $I_3$ and $I_4$, where $$I_1=I_3+I_4=\bf 0.75\;\rm A\tag 2$$ where $$12I_3=4I_4$$ Thus, $$I_4=3I_3$$ Plug into (2), $$ I_1=I_3+3I_3= 0.75\;\rm A$$ $$I_3=\bf \frac{3}{16}\;\rm A$$ and $$I_4=\bf \frac{9}{16}\;\rm A$$ \begin{array}{|c|c|c|} \hline R&I({\;\rm A})& \Delta V ({\;\rm V})\\ \hline 4\;\Omega & \frac{9}{16}=0.56& 2.25 \\ \hline 12\;\Omega & \frac{3}{16}=0.19& 2.25 \\ \hline 5\;\Omega & \frac{3}{4}=0.75& 3.75\\ \hline 24\;\Omega & \frac{1}{4}=0.25& 6\\ \hline 3\;\Omega & 1& 3\\ \hline \end{array}
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