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

$$I = \frac{100\,\text{W}}{120\,\text{V}} = 0.833\,\text{A}$$

Q: A circuit contains a 9 V battery and two resistors, $$R_1 = 12$$\,\Omega$$ and R_2$ = 6\,\Omega$$, in series. What is the current in the circuit?

$$I = \frac{9\,\text{V}}{12\,\Omega + 6\,\Omega} = 0.5\,\text{A}$$

Q: A 4000 W electric water heater runs for 10 hours. How much energy does it use in kilowatt-hours (kWh)?

$$4000\,\text{W} \times 10\,\text{h} = 40\,\text{kWh}$$

Q: A stereo amplifier can deliver a maximum power of 100 W to an 8 $$\Omega$$ loudspeaker. What is the maximum current?

$$I_{max} = \sqrt{\frac{100\,\text{W}}{8\,\Omega}} = 3.5\,\text{A}$$

Question 1

Which of the following statements best describes Kirchhoff’s Junction Law?

Accepted Answer

The total current entering a junction equals the total current leaving the junction: $$\sum I_{in} = \sum I_{out}$$

Question 2

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

Accepted Answer

$$I = \frac{100\,	ext{W}}{120\,	ext{V}} = 0.833\,	ext{A}$$

Question 3

Which of the following is true for resistors connected in parallel?

Accepted Answer

The potential difference across each resistor is the same.

Question 4

A circuit contains a 9 V battery and two resistors, $$R_1 = 12$$\,\Omega$$ and R_2$ = 6\,\Omega$$, in series. What is the current in the circuit?

Accepted Answer

$$I = \frac{9\,	ext{V}}{12\,\Omega + 6\,\Omega} = 0.5\,	ext{A}$$

Question 5

Which has a larger resistance: a 60 W lightbulb or a 100 W lightbulb, both rated for 120 V?

Accepted Answer

The 60 W bulb

Question 6

A 4000 W electric water heater runs for 10 hours. How much energy does it use in kilowatt-hours (kWh)?

Accepted Answer

$$4000\,	ext{W} 	imes 10\,	ext{h} = 40\,	ext{kWh}$$

Question 7

In a series circuit with three resistors ($$R_1 = 15$$\,\Omega$$, R_2$ = 4\,\Omega$$, $$R_3 = 8$$\,\Omega$$) and a 9 V battery, what is the equivalent resistance?

Accepted Answer

$$R_{eq} = 15\,\Omega + 4\,\Omega + 8\,\Omega = 27\,\Omega$$

Question 8

A circuit contains a 9 V battery and two resistors, $$R_1 = 9$$\,\Omega$$ and R_2$ = 1\,\Omega$$, in parallel. What is the equivalent resistance?

Accepted Answer

$$R_{eq} = \frac{1}{\frac{1}{9} + \frac{1}{1}} = 0.9\,\Omega$$

Question 9

Which equation correctly expresses the power dissipated by a resistor in terms of the potential drop across it?

Accepted Answer

$$P = \frac{(\Delta V)^2$}{R}$$

Question 10

A voltmeter is used to measure the potential difference across a resistor in a circuit. How should it be connected?

Accepted Answer

In parallel with the resistor

Question 11

A circuit contains a 30 V battery and two resistors, $$R_1 = 10$$\,\Omega$$ and R_2$ = 5\,\Omega$$, in series. What is the potential difference across $$R_1$$?

Accepted Answer

$$V_{R_1$} = 20\,	ext{V}$$

Question 12

If a switch is closed in a parallel branch of a circuit, what happens to the total current supplied by the battery?

Accepted Answer

It increases.

Question 13

Which of the following is a correct application of Kirchhoff’s Loop Law?

Accepted Answer

The sum of all potential differences around a closed loop is zero: $$\sum \Delta V = 0$$

Question 14

A stereo amplifier can deliver a maximum power of 100 W to an 8 $$\Omega$$ loudspeaker. What is the maximum current?

Accepted Answer

$$I_{max} = \sqrt{\frac{100\,	ext{W}}{8\,\Omega}} = 3.5\,	ext{A}$$

Question 15

In a parallel circuit with a 9 V battery and resistors $$R_1 = 15$$\,\Omega$$, R_2$ = 4\,\Omega$$, and $$R_3 = 8$$\,\Omega$$, what is the total current supplied by the battery?

Accepted Answer

$$I = \frac{9\,	ext{V}}{2.26\,\Omega} = 3.98\,	ext{A}$$

Question 16

Which resistor dissipates more power in a parallel circuit with a 9 V battery: a 9 $$\Omega$$ resistor or a 1 $$\Omega$$ resistor?

Accepted Answer

The 1 $$\Omega$$ resistor

Question 17

A circuit contains three identical bulbs and two identical batteries. If bulb A is in a separate loop and bulbs B and C are in series in another loop, which bulb is brightest?

Accepted Answer

Bulb A

Question 18

What is the correct formula for the equivalent resistance of $$N$$ resistors in parallel?

Accepted Answer

$$\frac{1}{R_{eq}} = \frac{1}{R_1$} + \frac{1}{R_2$} + ... + \frac{1}{R_N}$$

Fundamentals of Electric Circuits: Series and Parallel Resistor Networks

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