A 190-pF capacitor and a 760-pF capacitor are both charged to 1.30 kV. They are then disconnected from the voltage source and are connected together, positive plate to negative plate and negative plate to positive plate. (a) Find the resulting potential difference across each capacitor. V190 pF = kV V760 pF = kV (b) Find the energy lost when the connections are made. eBook

A 190-pF capacitor and a 760-pF capacitor are both charged to 1.30 kV. They are then disconnected from the voltage source and are connected together, positive plate to negative plate and negative plate to positive plate. (a) Find the resulting potential difference across each capacitor. V190 pF = kV V760 pF = kV (b) Find the energy lost when the connections are made. eBook

Principles of Physics: A Calculus-Based Text

5th Edition

ISBN:9781133104261

Author:Raymond A. Serway, John W. Jewett

Publisher:Raymond A. Serway, John W. Jewett

Chapter20: Electric Potential And Capacitance

Section: Chapter Questions

Problem 43P

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According to UE=12C(V)2 (Eq. 27.3), a greater capacitance means more energy is stored by the capacitor, but according to UE = Q2/2C (Eq. 27.2), a greater capacitance means less energy is stored. How can both of these equations be correct?
Suppose that the capacitance of a variable capacitor can be manually changed from 100 pF to 800 pF by turning a dial, connected to one set of plates by a shaft from 0° to 180°. With the dial set at 180° (corresponding to C — 800 pF), the capacitor is connected to a 500-V source. After charging, the capacitor is disconnected from the source, and the dial is turned to 0°. If friction is negligible, how much work is required to turn the dial from 180° to 0°?
When a Leyden jar is charged by a hand generator (Fig. 27.1, page 828), the work done by the person turning the crank is stored as electric potential energy in the jar. When a capacitor is charged by a battery, where does the electric potential energy come from?
A 10.0-F capacitor is charged to 15.0 V. It is next connected in series with an uncharged 5.00-F capacitor. The series combination is finally connected across a 50.0-V battery as diagrammed in Figure P26.63. Find the new potential differences across the 5.00-F and 10.0-F capacitors after the switch is thrown closed.
According to its design specification, the timer circuit delaying the closing of an elevator door is to have a capacitance of 32.0 F between two points A and B. When one circuit is being constructed, the inexpensive but durable capacitor installed between these two points is found to have capacitance 34.8 F. To meet the specification, one additional capacitor can be placed between the two points. (a) Should it be in series or in parallel with the 34.8-F capacitor? (b) What should be its capacitance? (c) What If? The next circuit comes down the assembly line with capacitance 29.8 F between A and B. To meet the specification, what additional capacitor should be installed in series or in parallel in that circuit?
A 2.0F capacitor and a 4.0F capacitor are connected in series across a 1.0-kV potential. The charged capacitors are then disconnected from the source and connected to each other with terminals of like sign together. Find the charge on each capacitor and the voltage across each capacitor.
When discharging a capacitor, as discussed in conjunction with Figure 21.39, how long does it take for the voltage on the capacitor to reach zero? Is this a problem?
A 10.0-F capacitor is charged to 15.0 V. It is next connected in series with an uncharged 5.00-F capacitor. The series combination is finally connected across a 50.0-V battery as diagrammed in Figure P20.83. Find the new potential differences across the 5.00-F and 10.0-F capacitors after the switch is thrown closed. Figure P20.83
A variable air capacitor used in a radio tuning circuit is made of N semicircular plates, each of radius R and positioned a distance d from its neighbors, to which it is electrically connected. As shown in Figure P20.38, a second identical set of plates is enmeshed with the first set. Each plate in the second set is halfway between two plates of the first set. The second set can rotate as a unit. Determine the capacitance as a function of the angle of rotation , where = 0 corresponds to the maximum capacitance. Figure P20.38
(i) Rank the following five capacitors from greatest to smallest capacitance, noting any cases of equality, (a) a 20-F capacitor with a 4-V potential difference between its plates (b) a 30-F capacitor with charges of magnitude 90 C on each plate (c) a capacitor with charges of magnitude 80 C on its plates, differing by 2 V in potential. (d) a 10-F capacitor storing energy 125 J (e) a capacitor storing energy 250 J with a 10-V potential difference (ii) Rank the same capacitors in part (i) from largest to smallest according to the potential difference between the plates, (iii) Rank the capacitors in part (i) in the order of the magnitudes of the charges on their plates, (iv) Rank the capacitors in part (i) in the order of the energy they store.
Two capacitors, C1 = 18.0 F and C2 = 36.0 F, are connected in series, and a 12.0-V battery is connected across the two capacitors. Find (a) the equivalent capacitance and (b) the energy stored in this equivalent capacitance. (c) Find the energy stored in each individual capacitor. (d) Show that the sum of these two energies is the same as the energy found in part (b). (e) Will this equality always be true, or docs it depend on the number of capacitors and their capacitances? (f) If the same capacitors were connected in parallel, what potential difference would be required across them so that the combination stores the same energy as in part (a)? (g) Which capacitor stores more energy in this situation, C1 or C2?
Two capacitors, C1 = 18.0 F and C2 = 36.0 F, are connected in series, and a 12.0-V battery is connected across them. (a) Find the equivalent capacitance, and the energy contained in this equivalent capacitor. (b) Find the energy stored in each individual capacitor. Show that the sum of these two energies is the same as the energy found in part (a). Will this equality always be true, or does it depend on the number of capacitors and their capacitances? (c) If the same capacitors were connected in parallel, what potential difference would be required across them so that the combination stores the same energy' as in part (a)? Which capacitor stores more energy in this situation, C1 or C2?