(a)
The potential difference across the capacitor.
(a)
Answer to Problem 43P
The potential difference across the capacitor is
Explanation of Solution
Let the resistance across
When the circuit is connected with a voltage source, the capacitor starts to charge. So, it acts as an open circuit as shown in figure below.
Figure (1)
Write the expression for the equivalent resistance when the resistors are connected in series.
Here, the equivalent resistance is
Write the expression to current through the series connection..
Here,
Write the expression to determine the potential difference
Write the expression to determine the potential difference
using the voltage division rule.
Write the expression to determine the potential difference across the capacitor.
Here,
Conclusion:
Substitute
Substitute
Substitute
Substitute
Substitute
Therefore, the potential difference across the capacitor is
(b)
The time interval at which the capacitor discharges to one tenth of its initial voltage.
(b)
Answer to Problem 43P
The time interval at which the capacitor discharges to one tenth of its initial voltage is
Explanation of Solution
When the battery is disconnected, the capacitor starts discharging acting as a voltage source.
The circuit diagram is shown below after the battery is disconnected.
Figure (2)
The resistors
Write the expression for the equivalent resistance when the resistors are connected in series.
Here, the equivalent resistance is
Also, the resistors
Write the expression for the equivalent resistance when the resistors are connected in series.
Here, the equivalent resistance is
Now the resistors
Write the expression for the equivalent resistance when the resistors are connected in parallel.
Here, the equivalent resistance for the parallel connection is
Write the expression to calculate the time interval at which the capacitor discharges to one tenth of its initial voltage.
Here,
Substitute
Conclusion:
Substitute
Substitute
Substitute
Substitute
Therefore, the time interval at which the capacitor discharge to one tenth of its initial voltage is
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Chapter 28 Solutions
Physics for Scientists and Engineers with Modern Physics, Technology Update
- (a) Determine the equilibrium charge on the capacitor in the circuit of Figure P27.46 as a function of R. (b) Evaluate the charge when R = 10.0 . (c) Can the charge on the capacitor be zero? If so, for what value of R? (d) What is the maximum possible magnitude of the charge on the capacitor? For what value of R is it achieved? (c) Is it experimentally meaningful to take R = ? Explain your answer. If so, what charge magnitude does it imply? Figure P27.46arrow_forwardA charge Q is placed on a capacitor of capacitance C. The capacitor is connected into the circuit shown in Figure P26.37, with an open switch, a resistor, and an initially uncharged capacitor of capacitance 3C. The switch is then closed, and the circuit comes to equilibrium. In terms of Q and C, find (a) the final potential difference between the plates of each capacitor, (b) the charge on each capacitor, and (c) the final energy stored in each capacitor. (d) Find the internal energy appearing in the resistor. Figure P26.37arrow_forwardA Pairs of parallel wires or coaxial cables are two conductors separated by an insulator, so they have a capacitance. For a given cable, the capacitance is independent of the length if the cable is very long. A typical circuit model of a cable is shown in Figure P27.87. It is called a lumped-parameter model and represents how a unit length of the cable behaves. Find the equivalent capacitance of a. one unit length (Fig. P27.87A), b. two unit lengths (Fig. P27.87B), and c. an infinite number of unit lengths (Fig. P27.87C). Hint: For the infinite number of units, adding one more unit at the beginning does not change the equivalent capacitance.arrow_forward
- A battery is used to charge a capacitor through a resistor as shown in Figure P27.44. Show that half the energy supplied by the battery appears as internal energy in the resistor and half is stored in the capacitor. Figure P27.44arrow_forwardThe circuit in Figure P27.85 shows four capacitors connected to a battery. The switch S is initially open, and all capacitors have reached their final charge. The capacitances are C1 = 6.00 F, C2 = 12.00 F, C3 = 8.00 F, and C4 = 4.00 F. a. Find the potential difference across each capacitor and the charge stored in each. b. The switch is now closed. What is the new final potential difference across each capacitor and the new charge stored in each? Figure P27.85arrow_forwardThe circuit shown in Figure P28.78 is set up in the laboratory to measure an unknown capacitance C in series with a resistance R = 10.0 M powered by a battery whose emf is 6.19 V. The data given in the table are the measured voltages across the capacitor as a function of lime, where t = 0 represents the instant at which the switch is thrown to position b. (a) Construct a graph of In (/v) versus I and perform a linear least-squares fit to the data, (b) From the slope of your graph, obtain a value for the time constant of the circuit and a value for the capacitance. v(V) t(s) In (/v) 6.19 0 5.56 4.87 4.93 11.1 4.34 19.4 3.72 30.8 3.09 46.6 2.47 67.3 1.83 102.2arrow_forward
- A pair of capacitors with capacitances CA = 3.70 F and CB = 6.40 F are connected in a network. What is the equivalent capacitance of the pair of capacitors if they are connected a. in parallel and b. in series?arrow_forwardThe- pair of capacitors in Figure P28.63 are fully charged by a 12.0-V battery. The battery is disconnected, and the switch is then closed. Alter 1.00 ms has elapsed, (a) how much charge remains 011 the 3.00-F capacitor? (b) How much charge remains on the 2.00-F capacitor? (c) What is the current in the resistor at this time?arrow_forwardFigure P27.75 shows four capacitors with CA = 4.00 F, CB = 8.00 F. CC = 6.00 F. and CD = 5.00 F connected across points a and b, which have potential difference Vab = 12.0 V. a. What is the equivalent capacitance of the four capacitors? b. What is the charge on each of the four capacitors?arrow_forward
- A capacitor with initial charge Q0 is connected across a resistor R at time t = 0. The separation between the plates of the capacitor changes as d = d0/(1 + t) for 0 t 1 s. Find an expression for the voltage drop across the capacitor as a function of time.arrow_forwardConsider the circuit shown in Figure P20.52, where C1 = 6.00 F, C2 = 3.00 F, and V = 20.0 V. Capacitor C1 is first charged by closing switch S1. Switch S1 is then opened, and the charged capacitor is connected to the uncharged capacitor by closing S2. Calculate (a) the initial charge acquired by C1 and (b) the final charge on each capacitor. Figure P20.52arrow_forwardAn oceanographer is studying how the ion concentration in seawater depends on depth. She makes a measurement by lowering into the water a pair of concentric metallic cylinders (Fig. P21.66) at the end of a cable and taking data to determine the resistance between these electrodes as a function of depth. The water between the two cylinders forms a cylindrical shell of inner radius ra, outer radius rb, and length L much larger than rb. The scientist applies a potential difference V between the inner and outer surfaces, producing an outward radial current I. Let represent the resistivity of the water. (a) Find the resistance of the water between the cylinders in terms of L, , ra, an rb. (b) Express the resistivity of the water in terms of the measured quantities L, ra, rb, V, and I. Figure P21.66arrow_forward
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