Q: A 6 $$\Omega$$ flashlight bulb is powered by a 3 V battery with an internal resistance of 1 $$\Omega. $$What is the terminal voltage of the battery when the bulb is on?

$$V_{\text{terminal}} = 2.6\ \mathrm{V}$$

Q: A capacitor in an RC circuit is discharging. If the resistance is decreased, what happens to the rate at which the capacitor discharges?

It discharges more quickly because the time constant $$\tau = RC is $$smaller.

Question 1

A 12 V car battery has an internal resistance of $$0.020\ \Omega. If $$the battery is accidentally short-circuited with a thick wire (negligible resistance), what is the current through the wire, and what is the power dissipated inside the battery?

Accepted Answer

Current: $$600\ \mathrm{A}$$, Power: $$7200\ \mathrm{W}$$

Question 2

Which of the following statements about resistors in parallel is correct?

Accepted Answer

The equivalent resistance is less than any individual resistor in the group.

Question 3

A 100 W incandescent lightbulb is connected to a 120 V outlet. What is the current through the bulb?

Accepted Answer

$$I = \dfrac{P}{V} = \dfrac{100\ \mathrm{W}}{120\ \mathrm{V}} = 0.833\ \mathrm{A}$$

Question 4

In an RC circuit, the time constant $$	au is $$given by which of the following expressions?

Accepted Answer

$$	au = RC$$

Question 5

A 6 $$\Omega$$ flashlight bulb is powered by a 3 V battery with an internal resistance of 1 $$\Omega. $$What is the terminal voltage of the battery when the bulb is on?

Accepted Answer

$$V_{	ext{terminal}} = 2.6\ \mathrm{V}$$

Question 6

Which of the following best describes Kirchhoff’s loop law?

Accepted Answer

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

Question 7

A circuit contains three resistors in series: $$R_1 = 2$$\ \Omega$$, R_2$ = 3\ \Omega$$, and $$R_3 = 5$$\ \Omega$$. What is the equivalent resistance?

Accepted Answer

$$R_{	ext{eq}} = 10\ \Omega$$

Question 8

A 60 W and a 100 W lightbulb are both rated for 120 V and are connected in parallel to a 120 V source. Which bulb has the greater resistance?

Accepted Answer

The 60 W bulb

Question 9

Immediately after closing the switch in an RC charging circuit with an initially uncharged capacitor, what is the voltage across the capacitor?

Accepted Answer

$$0\ \mathrm{V}$$

Question 10

Which of the following is a correct application of Kirchhoff’s junction law?

Accepted Answer

The total current entering a junction equals the total current leaving the junction.

Question 11

A circuit consists of a 9 V battery and three resistors in parallel: $$R_1 = 2$$\ \Omega$$, R_2$ = 3\ \Omega$$, $$R_3 = 6$$\ \Omega$$. What is the total current supplied by the battery?

Accepted Answer

$$I = 3.98\ \mathrm{A}$$

Question 12

Which of the following best describes the behavior of a voltmeter and an ammeter in a circuit?

Accepted Answer

A voltmeter is connected in parallel and has very high resistance; an ammeter is connected in series and has very low resistance.

Question 13

A capacitor in an RC circuit is discharging. If the resistance is decreased, what happens to the rate at which the capacitor discharges?

Accepted Answer

It discharges more quickly because the time constant $$	au = RC is $$smaller.

Question 14

Which of the following is true about the current through resistors in series?

Accepted Answer

The current is the same through all resistors in series.

Question 15

A 1500 W hair dryer is used for 10 minutes. How much energy does it consume in kilowatt-hours?

Accepted Answer

$$0.25\ \mathrm{kWh}$$

Question 16

Which of the following materials are considered ohmic?

Accepted Answer

Wires and resistors

Question 17

A circuit is grounded at a point between two resistors in series. What is the effect on the potential at other points in the circuit?

Accepted Answer

The potential at each point is shifted by a constant, but potential differences remain unchanged.

Question 18

In a discharging RC circuit, the charge on the capacitor as a function of time is given by:

Accepted Answer

$$Q(t) = Q_0$ e$$^{-t/RC}$$

Question 19

A 4000 W electric water heater is used for 10 hours. How much energy does it use, and what would be the cost at $$0.10$$ per kWh?

Accepted Answer

Energy: $$40\ \mathrm{kWh}$$, Cost: $$\4.00$

Fundamentals of Electric Circuits: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards