Question 1

A parallel plate capacitor is connected to a battery that maintains a constant voltage $$V. If a $$dielectric with dielectric constant $$k is $$inserted between the plates, which of the following statements is true about the charge $$Q$$ and the energy $$U$$ stored in the capacitor?

Accepted Answer

Charge $$Q$$ increases by a factor of $$k$$, and energy $$U$$ increases by a factor of $$k.$$

Question 2

Which equation correctly defines the capacitance $$C of a $$parallel plate capacitor with plate area $$A$$, separation $$d$$, and dielectric constant $$k$$?

Accepted Answer

$$C = \frac{k \$$epsilon_0$$ A}{d}$$

Question 3

A circuit contains three resistors: $$R_1 = 2$$\,\Omega$$, R_2$ = 4\,\Omega$$, and $$R_3 = 6$$\,\Omega$$ connected in parallel. What is the equivalent resistance R$$_{eq}$$ of the circuit?

Accepted Answer

$$R_{eq} = 1.09\,\Omega$$

Question 4

A battery with emf $$\mathcal{E}$$ and internal resistance $$r is $$connected to an external resistor $$R. $$What is the current $$I in $$the circuit?

Accepted Answer

$$I = \frac{\mathcal{E}}{R + r}$$

Question 5

Which of the following best describes the atomic view of current in a metal wire?

Accepted Answer

Electrons drift opposite to the electric field, superimposed on random thermal motion.

Question 6

A capacitor is charged to a voltage $$V_0$$ and then disconnected from the battery. If a dielectric is inserted, what happens to the energy stored in the capacitor?

Accepted Answer

The energy decreases by a factor of $$k.$$

Question 7

Which formula gives the energy $$U$$ stored in a capacitor with capacitance $$C$$ and voltage $$V$$?

Accepted Answer

$$U = \frac{1}{2}CV^2$

Question 8

A cylindrical capacitor consists of two coaxial cylinders of length $$L$$, inner radius $$a$$, and outer radius $$b. $$What is the capacitance $$C of $$this capacitor (in vacuum)?

Accepted Answer

$$C = \frac{2\pi \$$epsilon_0$$ L}{\ln(b/a)}$$

Question 9

In a DC circuit, a lightbulb rated at 60 W is connected to a 120 V source. What is the resistance of the lightbulb?

Accepted Answer

$$R = 240\,\Omega$$

Question 10

A resistor of $$10\,\Omega$$ and a capacitor of $$100\,\mu\mathrm{F}$$ are connected in series to a $$12\,\mathrm{V}$$ battery. What is the time constant $$	au of $$the circuit?

Accepted Answer

$$	au = 1\,\mathrm{s}$$

Question 11

Which of the following is the correct expression for the current $$I(t) in an RC $$circuit during charging, where $$I_0 is $$the initial current?

Accepted Answer

$$I(t) = I_0$ e$$^{-t/RC}$$

Question 12

Two capacitors, $$C_1 = 2$$\,\mu\mathrm{F}$$ and C_2$ = 4\,\mu\mathrm{F}$$, are connected in series. What is their equivalent capacitance?

Accepted Answer

$$C_{eq} = 1.33\,\mu\mathrm{F}$$

Question 13

A voltmeter is connected across a resistor in a circuit. Which property of the voltmeter is most important for accurate measurement?

Accepted Answer

It should have very high resistance.

Question 14

A wire has a resistivity $$\rho$$, length $$L$$, and cross-sectional area $$A. $$What is its resistance $$R$$?

Accepted Answer

$$R = \frac{\rho L}{A}$$

Question 15

In a circuit, three resistors $$R_1$$, $$R_2$$, and $$R_3$$ are connected in series. Which statement is true about the current through each resistor?

Accepted Answer

The current is the same through all resistors.

Question 16

A capacitor is connected to a battery and fully charged. The battery is then removed, and the capacitor is connected across a resistor. What is the voltage across the capacitor after a long time?

Accepted Answer

It is zero.

Question 17

Which of the following is Kirchhoff’s loop rule?

Accepted Answer

The sum of the potential differences around any closed loop is zero.

Question 18

A capacitor stores a charge $$Q at $$voltage $$V. $$Which equation defines its capacitance $$C$$?

Accepted Answer

$$C = \frac{Q}{V}$$

Question 19

A circuit contains a battery of emf $$\mathcal{E}$$, a resistor $$R$$, and a capacitor $$C in $$series. What is the voltage across the capacitor at time $$t$$ during charging?

Accepted Answer

$$V_C(t) = \mathcal{E} (1 - e$$^{-t/RC}$$)$$

Physics II Exam 2 Study Guide: Capacitance, DC Circuits, and Current

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