University Physics with Modern Physics (14th Edition)

Published by Pearson
ISBN 10: 0321973615
ISBN 13: 978-0-32197-361-0

Chapter 24 - Capacitance and Dielectrics - Problems - Exercises - Page 810: 24.29

Answer

(a) $Q_t = 24.2 \times 10^{3} \,\text{nC} $ (b) $Q_{35} = 7.7 \times 10^{3} \,\text{nC}$ and $Q_{75} = 16.5 \times 10^{3} \,\text{nC}$ (c) $U_{Parallel} = 2.6 \times 10^{-3} \,\text{J}$ (d) $ U_1 = 8.47 \times 10^{-3} \,\text{J} $ and $ U_2 = 18.15 \times 10^{-3} \,\text{J} $ (e) $V_1 = V_2 = 220 \,\text{V}$

Work Step by Step

(a) In parallel, the equivalent capacitance of both capacitors is given by $$C_{eq} = 35 \,\text{nF} + 75 \,\text{nF} = 110 \,\text{nF} $$ Therefore, the total charge of the network is given by $$Q_{t} = C_{eq}V = 110 \,\text{nF} \times 220 \,\text{V} = \boxed{24.2 \times 10^{3} \,\text{nC}} $$ (b) In parallel, the potential is the same therefore we could find the charge for each capacitor as next $$Q_{35}= C_{35} V = 35 \,\text{nF} \times 220 \,\text{V} = \boxed{7.7 \times 10^{3} \,\text{nC}} $$ $$Q_{75}= C_{75}V = 75\,\text{nF} \times 220 \,\text{V} = \boxed{16.5 \times 10^{3} \,\text{nC}} $$ (c) Their stored energy in parallel is given by $$U_{Parallel} = \dfrac{1}{2} C_{eq}V^2 = \dfrac{1}{2} (110 \times 10^{-9} \,\text{C})(220 \,\text{V})^2 = \boxed{2.6 \times 10^{-3} \,\text{J}}$$ (d) Their stored energy stored in each capacitor is given by: $$U_1 = \dfrac{1}{2} C_{1}V^2 = \dfrac{1}{2} (35 \times 10^{-9} \,\text{F})(220\,\text{V})^2 = \boxed{8.47 \times 10^{-3} \,\text{J}}$$ $$U_2 = \dfrac{1}{2} C_{2}V^2 = \dfrac{1}{2} (75 \times 10^{-9} \,\text{F})(220 \,\text{V})^2 = \boxed{18.15 \times 10^{-3} \,\text{J}}$$ (e) In parallel, both cacapictiors have the same potential of the total comibination $$\boxed{V_1 = V_2 = 220 \,\text{V}}$$
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