Capacitors

For the circuit shown, which of the following graphs shows the voltage in the resistor, VR, as a function of time, t?

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A capacitor is connected to a voltage source. The voltage source is set at a fixed value, and the spacing between the plates is gradually increased without disconnecting the capacitor from the voltage source. Which of the following is a correct claim about how this will affect the charge on the plates of the capacitor and provides evidence to support this claim?

• The charge on the plates of the capacitor will increase, because the capacitance increases.

• The charge on the plates of the capacitor will decrease, because the capacitance increases

• The charge on the plates of the capacitor will increase, because the capacitance decreases.

• The charge on the plates of the capacitor will decrease, because the capacitance decreases.

A capacitor with a dielectric of constant k is fully charged and then disconnected from power. The dielectric is then removed from the capacitor. Which of the following claims about removing the dielectric from the isolated capacitor is correct?

• The energy stored in the capacitor remains unchanged.

• The energy stored in the capacitor increases by a factor of k.

• The energy stored in the capacitor decreases by a factor of k.

• The capacitance of the capacitor increases by a factor of k.

A parallel plate capacitor is connected to a battery until fully charged. If the battery remains connected while the separation between the plates is increased, which of the following remains constant?

• Potential difference between the plates.

• Capacitance

• Magnitude of the charge on each plate.

• Electric field intensity in the region between the plates.

Two metal plates of area A and separated by a distance d are placed in parallel near each other to form a capacitor with capacitance C. The plates are connected to a voltage source with potential V and allowed to charge completely. The voltage is then removed, and the plates moved so that they are now separated by a distance 2d. Which of the following statements is true?

• The charge on the plates has changed, and the electric field between them has increased.

• The capacitance of the plates has decreased, and the energy stored in the capacitor has increased.

• The potential between the plates has increased, and the electric field between them has decreased.

• The capacitance of the plates has decreased, and the electric field between them has decreased.

A battery is connected to a capacitor in order to set up a potential difference across the plates. While the battery remains connected, a dielectric is inserted between the plates of the capacitor. Which of the following statements concerning the capacitor with the dielectric is false?

• The net electric field between the plates has increased.

• The amount of charge on the plates has increased.

• The capacitance of the capacitor has increased.

• The net electric field between the plates has increased.

Each of the following figures shows three identical capacitors connected to a battery. Which circuit shown takes the longest time to reach a steady-state?

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An uncharged 3.0 μF capacitor is placed in a circuit with an ideal battery,  two resistors, and an open switch S, as shown in the figure above. The switch is then closed. What is the current in the 20 Ω resistor immediately after the switch is closed?

• 0 A

• 1.0 A

• 3.0 A

• 1.5 A

An uncharged 3.0 μF capacitor is placed in a circuit with an ideal battery,  two resistors, and an open switch S, as shown in the figure above. The switch is then closed. What is the current in the 20 Ω resistor a long time after the switch is closed?

• 3.0 A

• 1.5 A

• 1.0 A

• 0 A

A capacitor stores energy U₁ when it holds charge Q. The same capacitor stores U₂ when it holds charge 16Q. What is the ratio U₂/U₁?

• 1

• 16

• 8

• 256