Q: A parallel-plate capacitor has plates of area $$0.020\ \mathrm{m}^2$$ separated by $$1.0\ \mathrm{mm} of $$air. What is its capacitance?

$$C = 1.8 \times 10$$^{-10}$$\ \mathrm{F}$$

Q: A $$2.0\ \mu\mathrm{F}$$ and a $$4.0\ \mu\mathrm{F}$$ capacitor are connected in parallel across a $$12\ \mathrm{V}$$ battery. What is the total energy stored in the capacitors?

$$U = 4.32 \times 10$$^{-4}$$\ \mathrm{J}$$

Q: A $$6.0\ \mu\mathrm{F}$$ capacitor is charged to $$30\ \mathrm{V}. $$How much energy is stored in the capacitor?

$$U = 2.7 \times 10$$^{-3}$$\ \mathrm{J}$$

Question 1

A plastic rod is rubbed with fur, and then brought near a small, uncharged metal sphere suspended by a thread. Which of the following best describes the process and result if the sphere is charged by induction using the four-step method?

Accepted Answer

The sphere acquires a net positive charge because electrons are repelled from the sphere to the ground, and the rod never touches the sphere.

Question 2

Which of the following statements about electric field lines and equipotential surfaces is correct?

Accepted Answer

Equipotential surfaces are always perpendicular to electric field lines.

Question 3

Two point charges, $$q_1 = +2.0$$ 	imes $$10^{-6}$$\ \mathrm{C}$$ and q_2$ = -3.0 	imes 10$$^{-6}$$\ \mathrm{C}$$, are separated by $$0.30\ \mathrm{m} in $$air. What is the magnitude of the electrostatic force between them?

Accepted Answer

$$F = 600\ \mathrm{N}$$

Question 4

A parallel-plate capacitor has plates of area $$0.020\ \mathrm{m}^2$$ separated by $$1.0\ \mathrm{mm} of $$air. What is its capacitance?

Accepted Answer

$$C = 1.8 	imes 10$$^{-10}$$\ \mathrm{F}$$

Question 5

A $$12\ \mathrm{V}$$ battery with internal resistance $$r = 1.0\ \Omega is $$connected to a $$5.0\ \Omega$$ external resistor. What is the terminal voltage across the battery?

Accepted Answer

$$V_{ab} = 11\ \mathrm{V}$$

Question 6

Which of the following best explains why metals are good conductors of electricity?

Accepted Answer

Metals have loosely bound electrons that can move freely throughout the material.

Question 7

A $$10\ \mu\mathrm{F}$$ and a $$20\ \mu\mathrm{F}$$ capacitor are connected in series across a $$100\ \mathrm{V}$$ battery. What is the equivalent capacitance of the combination?

Accepted Answer

$$C_{eq} = 6.7\ \mu\mathrm{F}$$

Question 8

A copper wire of length $$2.0\ \mathrm{m}$$ and cross-sectional area $$1.0 	imes 10$$^{-6}$$\ \mathrm{m}^2$$ has a resistivity $$ho = 1.72 	imes 10$$^{-8}$$\ \Omega\cdot\mathrm{m}. $$What is its resistance?

Accepted Answer

$$R = 0.034\ \Omega$$

Question 9

A $$100\ \Omega$$ resistor and a $$200\ \Omega$$ resistor are connected in parallel. What is the equivalent resistance?

Accepted Answer

$$R_{eq} = 66.7\ \Omega$$

Question 10

A $$5.0\ \mu\mathrm{F}$$ capacitor is charged to $$100\ \mathrm{V}$$ and then disconnected from the battery. If a dielectric with $$K = 2.0 is $$inserted between the plates, what happens to the stored energy?

Accepted Answer

The stored energy is halved.

Question 11

A $$10\ \mu\mathrm{F}$$ capacitor is charged through a $$1.0\ \mathrm{M}\Omega$$ resistor. What is the time constant $$	au$$ for this RC circuit?

Accepted Answer

$$	au = 10\ \mathrm{s}$$

Question 12

A $$2.0\ \mu\mathrm{F}$$ and a $$4.0\ \mu\mathrm{F}$$ capacitor are connected in parallel across a $$12\ \mathrm{V}$$ battery. What is the total energy stored in the capacitors?

Accepted Answer

$$U = 4.32 	imes 10$$^{-4}$$\ \mathrm{J}$$

Question 13

A $$9.0\ \mathrm{V}$$ battery is connected to a circuit with two resistors, $$R_1 = 100$$\ \Omega$$ and R_2$ = 200\ \Omega$$, in series. What is the current through the circuit?

Accepted Answer

$$I = 0.03\ \mathrm{A}$$

Question 14

Which of the following is true about the direction of conventional current and electron flow in a metal wire?

Accepted Answer

Conventional current is opposite to the direction of electron flow.

Question 15

A $$1.0\ \mathrm{A}$$ current flows through a resistor for $$5.0\ \mathrm{min}. $$How much charge passes through the resistor?

Accepted Answer

$$Q = 300\ \mathrm{C}$$

Question 16

A $$6.0\ \mu\mathrm{F}$$ capacitor is charged to $$30\ \mathrm{V}. $$How much energy is stored in the capacitor?

Accepted Answer

$$U = 2.7 	imes 10$$^{-3}$$\ \mathrm{J}$$

Question 17

A $$12\ \mathrm{V}$$ battery is connected to a circuit with a $$4.0\ \Omega$$ resistor and a $$6.0\ \Omega$$ resistor in parallel. What is the total current supplied by the battery?

Accepted Answer

$$I = 5.0\ \mathrm{A}$$

Question 18

Which of the following statements about the charging of a capacitor in an RC circuit is correct?

Accepted Answer

The charge on the capacitor approaches its maximum value asymptotically.

Question 19

A $$9.0\ \mathrm{V}$$ battery is connected to a $$3.0\ \Omega$$ resistor. How much power is dissipated in the resistor?

Accepted Answer

$$P = 27\ \mathrm{W}$$

Question 20

A $$2.0\ \mu\mathrm{F}$$ capacitor is charged to $$100\ \mathrm{V}$$ and then connected across a $$1.0\ \mathrm{M}\Omega$$ resistor. How long will it take for the charge to decrease to $$36.8\% of $$its initial value?

Accepted Answer

$$t = 2.0\ \mathrm{s}$$

Electric Charge, Electric Potential, and DC Circuits: Study Guide (Chapters 17–19)

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