Deck 21: Electric Current and Direct-Current Circuits

Question 1

Conventional current is the flow of positive charge from higher to lower potential.

Answer 1

True

Question 2

Four equal resistors connected in series have same current and same voltage across each resistor.

Answer 2

True

Question 3

Electron flow is in the direction of conventional current.

Answer 3

False

Question 4

The resistance of a superconductor is infinite once it goes into the superconductivity state.

Question 5

An RC circuit is connected across a DC voltage source through an open circuit and a switch. As soon as the switch is closed, the charge on the capacitor increases but the voltage across it decreases as a function of time.

Question 6

You are given a copper bar of dimensions 3 cm × 5 cm × 8 cm and asked to attach leads to it in order to make a resistor. If you want to achieve the smallest possible resistance, you should attach the leads to the opposite faces that measure

A) 3 cm × 5 cm.
B) 3 cm × 8 cm.
C) 5 cm × 8 cm.
D) Any pair of faces produces the same resistance.

Question 7

Capacitors in series share the same charge and capacitors in parallel share the same voltage.

Question 8

The electromotive force of a battery is the maximum potential difference between the terminals of the battery.

Question 9

List two conditions for producing an electric current in a circuit.

Question 10

Kirchhoff's voltage rule is an example of conservation of energy.

Question 11

Which one of the following is the correct expression for electric current?

A) I = ΔC/Δt
B) I = ΔR/Δt
C) I = ΔV/Δt
D) I = ΔQ/Δt
E) None of the other answers is correct.

Question 12

Four unequal resistors connected in series have same current but different voltages.

Question 13

A series circuit is a current divider and a parallel circuit is a voltage divider circuit.

Question 14

Which one of the following is the correct statement regarding the resistance?

A) The resistance of a conductor decreases with temperature.
B) The resistance of a semiconductor increases with temperature.
C) The resistance of a wire is directly proportional to the length of the wire.
D) All of the above statements are correct.
E) None of the above statements is correct.

Question 15

Four equal resistors connected across a DC voltage source in either series or parallel will have equal voltage drops across each resistor.

Question 16

A wire of resistivity ρ must be replaced in a circuit by a wire four times as long. If, however, the total resistance is to remain as before, the diameter of the new wire must

A) remain unchanged.
B) be two times smaller.
C) be four times smaller.
D) be two times larger.
E) be four times larger.

Question 17

An RC circuit is connected across a DC voltage source through an open switch. As soon as the switch is closed, the capacitor charges linearly as a function of time.

Question 18

Describe how a simple electric cell works.

Question 19

You are given a copper bar of dimensions 3 cm × 5 cm × 8 cm and asked to attach leads to it in order to make a resistor. If you want to achieve the largest possible resistance, you should attach the leads to the opposite faces that measure

A) 3 cm × 5 cm.
B) 3 cm × 8 cm.
C) 5 cm × 8 cm.
D) Any pair of faces produces the same resistance.

Question 20

The resistivity of the material of a wire is inversely proportional to the resistance of the wire.

Question 21

A capacitor C is connected in series with a resistor R across a battery and an open switch. If a second capacitor of capacitance 2C is connected in series to the first, the time constant of the new RC circuit will be

A) the same as before.
B) larger than before.
C) smaller than before.
D) variable.

Question 22

Kirchhoff's junction rule is a statement of

A) the law of conservation of momentum.
B) the law of conservation of charge.
C) the law of conservation of energy.
D) the law of conservation of angular momentum.
E) Newton's second law.

Question 23

The length of a certain wire is kept same while its radius is doubled. What is the change in the resistance of this wire?

A) It is doubled.
B) It is quadrupled.
C) It is reduced by a factor of 2.
D) It is reduced by a factor of 4.
E) It is reduced by a factor of 8.

Question 24

Four unequal resistors are connected in a series circuit. Which one of the following statements is correct about this circuit?

A) The total resistance is equal to any one of the resistors.
B) The total resistance is equal to average of the four resistors.
C) The total resistance is less than the smallest resistor.
D) The total resistance is less than the largest resistor.
E) The total resistance is more than the largest resistor.

Question 25

When the current through a resistor is increased by a factor of 4, the power dissipated by it

A) decreases by a factor of 4.
B) decreases by a factor of 16.
C) increases by a factor of 16.
D) increases by a factor of 4.
E) remain unchanged.

Question 26

FIGURE 21-2
Which of the following equations represents a Kirchhoff's voltage rule for the circuit shown in Figure 21-2?

A) -6 V + 2 V - (6Ω)i₃ = 0 V
B) +4 V - (8Ω) i₂ - (12Ω) i₁ = 0 V
C) -(8Ω) i₂ + 4 V + 6 V + (12Ω) i₁ = 0 V
D) +6 V - (12Ω) i₁ - (8Ω) i₂ + 4 V = 0 V
E) none of the above

Question 27

The length of a certain wire is doubled while its radius is kept constant. What is the change in the resistance of this wire?

A) It stays the same.
B) It is doubled.
C) It is tripled.
D) It is quadrupled.
E) It is reduced by a factor of 2.

Question 28

The length of a certain wire is doubled while the radius is reduced by a factor of 4. What is the change in the resistance of this wire?

A) It stays the same.
B) It is quadrupled.
C) It is increased by a factor of 32.
D) It is increased by a factor of 16.
E) It is increased by a factor of 8.

Question 29

The length of a certain wire is halved while the radius is doubled. What is the change in the resistance of this wire?

A) It stays the same.
B) It is reduced by a factor of 2.
C) It is reduced by a factor of 4.
D) It is reduced by a factor of 8.
E) It is quadrupled.

Question 30

The length of a certain wire is doubled and at the same time its radius is also doubled. What is the change in the resistance of this wire?

A) It stays the same.
B) It is doubled.
C) It is quadrupled.
D) It is reduced by a factor of 2.
E) It is reduced by a factor of 4.

Question 31

The length of a certain wire is doubled and at the same time its radius is increased by a factor of 4. What is the change in the resistance of this wire?

A) It is reduced by a factor of 8.
B) It increases by a factor of 8.
C) It is reduced by a factor of 4.
D) It increases by a factor of 4.
E) It stays the same.

Question 32

FIGURE 21-1
Identify the junction nodes in the circuit shown in Figure 21-1.

A) A and B
B) D and E
C) A and E
D) C and F
E) E and F

Question 33

An RC circuit is connected across a DC voltage source through an open switch. The switch is closed at t = 0 s. Which of the following is a correct statement regarding the circuit?

A) The capacitor charges to its maximum value in one time constant.
B) The capacitor charges to its maximum value in two time constants.
C) The resistor and the capacitor share the applied voltage equally as a function of time.
D) The current flows through the circuit even after the capacitor is fully charged.
E) Once the capacitor is fully charged, there is no current in the circuit.

Question 34

The length of a certain wire is doubled and at the same time its radius is tripled. What is the change in the resistance of this wire?

A) It stays the same.
B) It is reduced by a factor of 4.5.
C) It is doubled.
D) It is tripled.
E) It is quadrupled.

Question 35

Which one of the following is a correct statement for a number of resistors connected in series or parallel?

A) The total resistance in a series circuit decreases as more resistors are added.
B) The flow of current is different through resistors connected in a series circuit.
C) The voltage is different across resistors connected in a parallel circuit.
D) The total resistance in a parallel circuit decreases as more resistors are added.
E) None of the above statements is correct.

Question 36

An RC circuit is connected across a DC voltage source through an open switch. The switch is closed at t = 0 s. Which of the following is a correct statement regarding this circuit?

A) The charge on the capacitor after four time constants is about 98% of the maximum value.
B) The charge on the capacitor after one time constant is about 25% of its maximum value.
C) The charge on the capacitor after one time constant is about 50% of its maximum value.
D) The voltage on the capacitor after two time constants is about 14% of the maximum value.
E) The voltage on this capacitor after two time constants is about 100% of its maximum value.

Question 37

The length of a certain wire is doubled and at the same time its radius is reduced by a factor of 2. What is the change in the resistance of this wire?

A) It is doubled.
B) It is quadrupled.
C) It increases by a factor of 6.
D) It increases by a factor of 8.
E) It is reduced by a factor of 2.

Question 38

A capacitor C is connected in series with a resistor R across a battery and an open switch. If a second capacitor of capacitance 2C is connected in parallel to the first, the time constant of the new RC circuit will be

A) the same as before.
B) twice as large as before.
C) three times a large as before.
D) one-half as large as before.
E) one-fourth as large as before.

Question 39

Four unequal resistors are connected in a parallel circuit. Which one of the following statements is correct about this circuit?

A) The total resistance is less than the smallest resistor.
B) The total resistance is equal to the average of the resistance of all the resistors.
C) The total resistance is equal to average of the four resistors.
D) The total resistance is more than the largest resistor.
E) None of the other answers is correct.

Question 40

Kirchhoff's loop rule is a statement of

A) the law of conservation of momentum.
B) the law of conservation of charge.
C) the law of conservation of energy.
D) the law of conservation of angular momentum.
E) Newton's second law.

Question 41

An RC circuit consists of 2.0 MΩ in series with a capacitor. When connected to a battery, the capacitor becomes 25% charged in 1.5 seconds. What is the capacitance value?

Question 42

What potential difference is required to cause 2.0 A to flow through a resistance of 8.0 Ω?

Question 43

An electric device delivers a current of 5.0 A for 10 seconds. How many electrons flow through this device?

A) 0.20
B) 20
C) 2.0
D) 3.1 × 10²⁰
E) 31 × 10²⁰

Question 44

The resistivity of the material of a wire is 1.76 × 10^-8 Ωm. If the diameter of the wire is 2 × 10^-3 m and its length is 2 m, what is its resistance?

A) 112 Ω
B) 11.2 Ω
C) 1.12 Ω
D) 0.112 Ω
E) 0.0112 Ω

Question 45

The potential difference between the ends of a resistor is 9 V when a current of 1 A flows through it. What is the value of that resistor?

A) 9 Ω s
B) 9 Ω/s
C) 9 V∙s
D) 9 V/s
E) 9 Ω

Question 46

Two 100 W lightbulbs are to be connected to a 120 V source. What is the current, potential difference, and dissipated power for each when they are connected:
(a) in parallel (the normal arrangement)?
(b) in series?

Question 47

The resistance of a 100-cm wire of cross sectional area 2 × 10^-6 m² is 400 Ω. What is the resistivity of the material of this wire?

A) 0.8 × 10^-4 Ωm
B) 8 × 10^-4 Ωm
C) 0.8 × 10^-5 Ωm
D) 0.8 × 10^-6 Ωm
E) 8 × 10^-6 Ωm

Question 48

The power rating of a resistor is 0.800 W. The value of the resistor is 400 Ω.
(a) What is the maximum voltage?
(b) What is the maximum current it can draw?

Question 49

Two resistors in series equal 9.0 ohms total; but the same two resistors in parallel are equivalent to 2.0 ohms. What are the resistor values?

Question 50

What charge appears on the plates of a 2.00 μF capacitor when it is charged to

Question 51

A 2.0 μF capacitor is charged to 12. V and then discharged through 4 × 10⁶ Ω. How long will it take for the voltage across the capacitor to drop to 3.0 V?

Question 52

Four 20. Ω resistors are connected in parallel. What is the equivalent resistance?

Question 53

A combination of 2.0 Ω in series with 4.0 Ω is connected in parallel with 3.0 Ω. What is the equivalent resistance?

Question 54

A charge of 12. C passes through an electroplating apparatus in 2.0 min. What is the average current?

Question 55

If the internal resistance of my 1.5 volt battery is 0.50 ohms, what is the maximum possible power and current that can be delivered from it?

Question 56

A 10-A current flows for two minutes.
(a) How much charge has passed through this circuit?
(b) How many electrons have passed any point in the circuit?

Question 57

Capacitances of 10. μF and 20. μF are connected in parallel, and this pair is then connected in series with a 30. μF capacitor. What is the equivalent capacitance of this arrangement?

Question 58

Given 3 capacitors:
4.00 μF, 7.00 μF, and 9.00 μF; what is the equivalent capacity if they are connected in series?

Question 59

Consider a 1.40 kW hair dryer operated on 120. V. What is
(a) the current?
(b) its resistance?

Question 60

Given 3 capacitors:
4.00 μF, 7.00 μF, and 9.00 μF; what is the equivalent capacity if they are connected in parallel?

Question 61

A simple circuit has a total resistance of 30 Ω. If a 2.0-A current is maintained in this circuit, how much energy is dissipated in this circuit in 4.0 seconds?

A) 24 J
B) 4.8 J
C) 48 J
D) 480 J
E) 6.0 J

Question 62

FIGURE 21-3
A 4-Ω resistor is connected in parallel with a 12-Ω resistor and this combination is connected to a DC power supply with voltage V as shown in Figure 21-3. If the total current in this circuit is 2 A, what is the value of voltage V?

A) 2 V
B) 3 V
C) 6 V
D) 1.5 V
E) None of the other answers is correct.

Question 63

A 200-W light bulb is connected across 110 V. What current will flow through this bulb?

A) 0.90 A
B) 0.36 A
C) 0 A
D) 0.60 A
E) 1.8 A

Question 64

FIGURE 21-8
Five equal resistors, of value 2.0 Ω each, are connected as shown in Figure 21-8. What is the equivalent resistance of this circuit?

A) 1.0 Ω
B) 10.0 Ω
C) 2.0 Ω
D) 6.0 Ω
E) 0.40 Ω

Question 65

FIGURE 21-4
A 100 V DC signal is applied to four resistors as shown in Figure 21-4. The values of the resistors are 20 Ω, 40 Ω, 60 Ω, and 80 Ω. What is the voltage across the 40 Ω resistor?

A) 20 V
B) 40 V
C) 60 V
D) 80 V
E) 100 V

Question 66

A 100-W light bulb is connected to a 110-V source. What current flows through the lamp?

A) 1.1 A
B) 2.2 A
C) 3.3 A
D) 4.4 A
E) 0.91 A

Question 67

A 100-W light bulb is connected to a 110-V source. What is the resistance of this bulb?

A) 100 Ω
B) 8.00 × 10^-3 Ω
C) 6.00 × 10^-3 Ω
D) 121 Ω
E) 242 Ω

Question 68

FIGURE 21-6
Three resistors of values 2 Ω, 6 Ω and 12 Ω are connected across a 2.0-V DC voltage source as shown in Figure 21-6. What is the total current I flowing this circuit?

A) 0.70 A
B) 1.5 A
C) 2.0 A
D) 3.0 A
E) 6.0 A

Question 69

The resistivity of a 1.0 m long wire is 1.72 × 10^-8 Ωm and its cross sectional area is 2.0 × 10^-6 m². If the wire carries a current of 0.20 A, what is the voltage across the wire?

A) 17 mV
B) 0.90 mV
C) 1.7 mV
D) 10 mV
E) 90 mV

Question 70

FIGURE 21-9
A 4.0-Ω resistor is connected in parallel with a 12-Ω resistor and both of these are connected to a DC power supply with voltage V as shown in Figure 21-9. If the total current in this circuit is 2.0 A, what is the current through the 4.0-Ω resistor?

A) 2.0 A
B) 2.5 A
C) 0.5 A
D) 3.0 A
E) 1.5 A

Question 71

The power rating of a resistor is 0.80 W. If the value of the resistor is 400 Ω, what is the maximum current it can draw?

A) 45 mA
B) 18 mA
C) 4.4 mA
D) 2.0 mA
E) 320 mA

Question 72

Four resistors of 20 Ω, 40 Ω, 60 Ω, and 80 Ω are connected across a DC voltage source. If the current through this circuit is 0.5 A, what is the voltage applied to this circuit?

A) 20 V
B) 40 V
C) 60 V
D) 80 V
E) 100 V

Question 73

Four resistors of 20 Ω, 40 Ω, 60 Ω, and 80 Ω are connected across a 50-V DC source. What is the current through this circuit?

A) 0.25 A
B) 0.50 A
C) 0.75 A
D) 2.0 A
E) 4.0 A

Question 74

FIGURE 21-7
Three 2.0-Ω resistors are connected across the sides of an equilateral triangle ABC as shown in Figure 21-7. What is the equivalent resistance between any two points, AB, BC, or AC, of this circuit?

A) 2.0 Ω
B) 6.0 Ω
C) 4.3 Ω
D) 3.3 Ω
E) 1.3 Ω

Question 75

The power rating of a 400 Ω resistor is 0.25 W. What is the maximum voltage?

A) 10 V
B) 20 V
C) 30 V
D) 40 V
E) 50 V

Question 76

A light bulb operating at a voltage of 120 V has a resistance of 200 Ω. What is the power?

A) 100 W
B) 60 W
C) 72 W
D) 14 × 10^-3 W
E) 7.2 W

Question 77

The power rating of a resistor is 0.800 W. If the value of the resistor is 400 Ω, what is the maximum voltage?

A) 110 V
B) 17.9 V
C) 170 V
D) 1.80 V

Question 78

A 100-V DC signal is applied to a series circuit composed of four equal resistors 10 Ω each. What is the voltage across each resistor?

A) 10 V
B) 15 V
C) 20 V
D) 25 V
E) 50 V

Question 79

A light bulb operating at a voltage of 120 Volt has a power of 60 W. What is the current flowing through this bulb?

A) 1.5 A
B) 2.5 A
C) 0.5 A
D) 2 A
E) 1 A

Question 80

FIGURE 21-5
Three resistors of values 2 Ω, 6 Ω and 12 Ω are connected across a DC voltage source as shown in Figure 21-5. If the total current through the circuit is 2.0 A, what is the applied voltage?

A) 6.0 V
B) 3.0 V
C) 2.0 V
D) 2.7 V
E) 1.5 V