Deck 19: Electric Currents and Circuits

Question 1

When an electric current exists within a conducting wire, which of the following statements describes the condition of any accompanying electric field?

A) must be perpendicular to current flow
B) must be parallel to current flow
C) must be zero
D) must be anti-parallel (opposite direction) to current flow

Answer 1

must be parallel to current flow

Question 2

You measure a 20.0-V potential difference across a 5.00- $\Omega$ resistor. What is the current flowing through it?

A) 5.00 A
B) 4.00 A
C) 100 A
D) 1.00 A

Answer 2

4.00 A

Question 3

Two wires with the same resistance have the same diameter but different lengths. If wire 1 has length L₁ and wire 2 has length L₂, how do L₁ and L₂ compare if wire 1 is made from copper and wire 2 is made from aluminum? The resistivity of copper is 1.7 *10^-5 $\Omega$ ·m and the resistivity of aluminum is 2.82 *10^-5 $\Omega$ ·m.

A) L₁ = 0.36 L₂
B) L₁ = 2.8 L₂
C) L₁ = 0.60 L₂
D) L₁ = 1.7 L₂

Answer 3

L₁ = 1.7 L₂

Question 4

The current in an electron beam in a cathode-ray tube is measured to be 280 µA. How many electrons hit the screen in 50 s? (e = 1.6 *10 ^{- 19} C)

A) 2.2 * 10¹¹ electrons
B) 8.8 * 10¹⁶ electrons
C) 8.8* 10¹⁵ electrons
D) 2.2 * 10¹⁵ electrons

Question 5

A 12.6-V battery supplies a 2.0-A current for 2.0 minutes. What is the work done by the battery during this process?

A) 0 J
B) 3.0 * 10³ J
C) 2.5 *10² J
D) 1.5 *10⁴ J

Question 6

Wire A and Wire B are each carrying the same current. If the diameter of Wire A is half that of Wire B, how does the drift velocity v_dA in Wire A compare to that in Wire B?

A) v_dA = 4 v_dB
B) v_dA = 2 v_dB
C) v_dA = v_dB /2
D) v_dA = v_dB /4

Question 7

In a certain material there is a current of 16 A flowing through a surface to the left, and there is an equal amount of positive and negative charge passing through the surface producing the current. How much negative charge passes through the surface?

A) 16 C/s toward the left
B) 16 C/s toward the right
C) 8 C/s toward the right
D) 8 C/s toward the left

Question 8

The size of the electric current in a electrical conductor is a function of which of the following?

A) conductor cross sectional area
B) velocity of charge carriers
C) density of charge carriers
D) All of these choices are valid.

Question 9

Two cylindrical resistors are made of the same material and have the same resistance. The resistors, R₁ and R₂, have different radii, r₁ and r₂, and different lengths, L₁ and L₂. Which of the following relative values for radii and lengths would result in equal resistances?

A) r₁ = r₂ and 4L₁ = L₂
B) r₁ = r₂ and L₁ = 2L₂
C) 2r₁ = r₂ and 4L₁ = L₂
D) 2r₁ = r₂ and L₁ = 2L₂

Question 10

If a metallic wire of cross-sectional area 3.0 *10 ^{- 6} m² carries a current of 9.1 A and has a mobile charge density of 4.24 * 10²⁸ carriers/m³, what is the average drift velocity of the mobile charge carriers? (charge value = 1.6 *10 ^{- 19} C)

A) 3.4 * 10³ m/s
B) 1.7 * 10³ m/s
C) 4.5*10 ^{- 4} m/s
D) 1.5 *10 ^{- 4} m/s

Question 11

How long is a wire made from 200 cm³ of copper if its resistance is 8.5 ohms? The resistivity of copper is 1.7 *10^-5 $\Omega$ ·m.

A) 10 m
B) 2.2 *10² m
C) 7.1 m
D) 3.0 *10³ m

Question 12

When you flip a switch to turn on a light, the delay before the light turns on is determined by:

A) the speed of the electric field moving in the wire.
B) the drift speed of the electrons in the wire.
C) the number of electron collisions per second in the wire.
D) none of these, since the light comes on instantly.

Question 13

A lightbulb drawing a current of 0.60 A is run for 2.0 hours. How many electrons pass through the bulb during this process?

A)
B)
C)
D)

Question 14

A metallic conductor has a resistivity of 18 *10 ^{- 6} $\Omega$ m. What is the resistance of a piece that is 15 m long and has a uniform cross sectional area of 6.0 *10 ^{- 6} m²?

A) 0.056 $\Omega$
B) 45 $\Omega$
C) 90 $\Omega$
D) 160 $\Omega$

Question 15

A Nichrome wire has a radius of 0.50 mm and a resistivity of 1.5 *10 ^{- 6} $\Omega$ m. If the wire carries a current of 1.0 A, what is the potential difference per unit length along this wire?

A) 1.9 V/m
B) 0.95 V/m
C) 1.6 V/m
D) 0.003 V/m

Question 16

The unit of electric current, the ampere, is equivalent to which of the following?

A)" V/ $\Omega$ "
B) "V/s"
C) " $\Omega$ .m"
D) "V. $\Omega$ "

Question 17

A 300-A·h battery can deliver how many coulombs starting from a full charge?

A) 4.8 * 10³
B) 4.3 * 10⁴
C) 7.2 * 10⁵
D) 1.1 * 10⁶

Question 18

A 0.10-m long metal rod has a radius of 1.0 cm and a resistance of 3.2 * 10 ^{- 5} $\Omega$ . What is the resistivity of the metal?

A) 5.0 *10 ^{- 8} $\Omega$ .m
B) 160*10 ^{- 8} $\Omega$ .m
C) 10 *10 ^{- 8} $\Omega$ .m
D) 1.6 *10 ^{- 8} $\Omega$ .m

Question 19

If the current in a wire is halved, what effect does this have on the electron drift velocity in the wire?

A) It decreases by a factor of two.
B) It increases by a factor of four.
C) It stays the same.
D) It doubles.

Question 20

A wire carries a steady current of 0.1 A over a period of 200 s. What total charge passes through the wire in this time interval?

A) 2 C
B) 200 C
C) 0.005 C
D) 20 C

Question 21

A 100-W light bulb is in a socket supplied with 120 V. What is the current in the bulb?

A) 7200 A
B) 0.83 A
C) 1.4 A
D) 0.50 A

Question 22

The unit for rate of energy transformation, the watt, in an electric circuit is equivalent to which of the following?

A) A. $\Omega$
B) V/s
C) V/ $\Omega$
D) V.A

Question 23

A high-voltage transmission line carries 500 A at 700,000 V. What is the power carried by the line?

A) 100 MW
B) 350 MW
C) 700 MW
D) 70 MW

Question 24

A copper cable needs to carry a current of 200 A with a power loss of only 1.5 W/m. What is the required radius of the copper cable? (The resistivity of copper is 1.7 *10 ^{- 8} $\Omega$ m.)

A) 4.0 cm
B) 0.21 cm
C) 0.85 cm
D) 1.2 cm

Question 25

A length L of wire has a voltage V across its ends while a current I runs through the wire. If a voltage 3V were applied to another length of this same wire from the same coil and the same current were found to run through it, what is the length of this second wire?

A)
B)
C)
D)

Question 26

If a 9.0-V battery, with negligible internal resistance, and an 27- $\Omega$ resistor are connected in series, what is the amount of electrical energy transformed to heat per coulomb of charge that flows through the circuit?

A) 0.50 J
B) 9.0 J
C) 3.0 J
D) 72 J

Question 27

A high-voltage transmission line carries 500 A at 700 kV for a distance of 100 miles. If the resistance in the wire is 1 $\Omega$ /mile, what is the power loss due to resistive losses?

A) 250 MW
B) 2.5 kW
C) 25 MW
D) 25 kW

Question 28

An electric clothes dryer draws 20 A at 220 V. If the clothes put into the dryer have a mass of 7.0 kg when wet and 3.0 kg dry, how long does it take to dry the clothes? (Assume all heat energy goes into vaporizing water, L_v = 2.26 *10⁶ J/kg.)

A) 55 min
B) 26 min
C) 16 min
D) 34 min

Question 29

If a lamp has resistance of 120 $\Omega$ when it operates at 200 W, what is the applied voltage?

A) 120 V
B) 220 V
C) 110 V
D) 155 V

Question 30

A resistor is connected to a battery with negligible internal resistance. If you replace the resistor with one that has quadruple the resistance, by what factor does the power dissipated in the circuit change?

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

Question 31

The quantity volt is equivalent to which of the following?

A) J/C
B) C/ $\Omega$
C) J.C
D) J.m

Question 32

An electric car is designed to run off a bank of 12-V batteries with total energy storage of 6.0 *10⁷ J. If the electric motor draws 6000 W in moving the car at a steady speed of 10 m/s, how far will the car go before it is "out of juice?"

A) 150 km
B) 50 km
C) 100 km
D) 25 km

Question 33

A light bulb, sold as long-lasting, is rated 120 W at 130 V. The "increased" lifetime comes from using it at 120 V. Assuming negligible change in resistance at the different voltage, what is its power consumption at 120 V?

A) 92 W
B) 102 W
C) 108 W
D) 85 W

Question 34

Ten coulombs of charge start from the negative terminal of a battery, flow through the battery and then leave the positive terminal through a wire, flow through a resistor, and then return to the starting point on this closed circuit. In this complete process, the ten coulombs:

A) receive heat energy from the resistor.
B) do positive work on the battery.
C) have a net loss of potential energy.
D) have no net change in potential energy.

Question 35

A wire of length L is uniformly stretched to triple its original length.By what factor does its resistance change?

A) 1, i.e., no change
B) 3
C) 9
D)

Question 36

A water pump draws about 4.4 A when connected to 240 V. What is the cost (with electrical energy at 9 cents per kWh) of running the pump for 10 h?

A) 82 cents
B) 8.0 cents
C) 95 cents
D) 15 cents

Question 37

If a light bulb has half the resistance of a 50-W lightbulb, what would be its wattage? Assume both bulbs are attached to the same 120-V circuit.

A) More information is needed.
B) 25 W
C) 200 W
D) 100 W

Question 38

Three wires of the same diameter and length are made from three different metals: copper ( ), aluminum ( ), and silver ( ). Which wire has the least resistance?

A) the aluminum wire
B) the silver wire
C) the copper wire
D) Since insufficient information is given to find the resistance of each wire, one cannot find the answer.

Question 39

Which process will double the power given off by a resistor?

A) doubling the current while making the voltage half as big
B) doubling the current while doubling the resistance
C) doubling the current by doubling the voltage
D) doubling the current by making a resistance half as big

Question 40

If a 500-W heater carries a current of 2.00 A, what is the voltage across the ends of the heating element?

A) 2000 V
B) 125 V
C) 0.008 V
D) 250 V

Question 41

If R₁ < R₂ < R₃, and if these resistors are connected in series in a circuit, which one dissipates the greatest power?

A) R₁
B) R₃
C) R₂
D) All are equal in power dissipation.

Question 42

Three resistors, each of different value, are used in a circuit with a power source supplying 12 volts. For which of the following resistor combinations is the total power supplied the greatest?

A) This cannot be found until it is known which resistor is in series with the parallel pair.
B) all three resistors in series
C) two of the resistors in parallel with the third resistor in series with the parallel pair
D) all three resistors in parallel

Question 43

An 10.0- $\Omega$ resistor is dissipating 100 watts. What are the current through it and the difference of potential across it?

A) 31.6 A, 3.16 V
B) 10.0 A, 3.16 V
C) 3.16 A, 31.6 V
D) 3.16 A, 10.0 V

Question 44

Two resistors of values 6.0 and 12.0 $\Omega$ are connected in parallel. This combination in turn is hooked in series with a 4.0- $\Omega$ resistor and a 24-V battery. What is the current in the battery?

A) 12 A
B) 3.0 A
C) 2.0 A
D) 6.0 A

Question 45

Three resistors with values R₁, R₂, and R₃, respectively, are connected in parallel. Which of the following expresses the total resistance, R_T, of the three resistors when connected in parallel?

A) R_T = (1/R₁ + 1/R₂ + 1/R₃)
B) R_T = R₁ = R₂ = R₃
C) R_T = R₁ + R₂ + R₃
D) R_T = (1/R₁ + 1/R₂ + 1/R₃) ^{- 1}

Question 46

Which two resistors are in parallel with each other?

A) R₂ and R₃
B) R and R₁
C) R₂ and R₄
D) R and R₄

Question 47

When a 24.0- $\Omega$ resistor is connected across a 12.0-V battery, a current of 410 mA flows. What is the internal resistance of the battery?

A) 29.3 $\Omega$
B) 0.9 $\Omega$
C) 5.3 $\Omega$
D) 0.02 $\Omega$

Question 48

Three resistors connected in parallel each carry currents labeled I₁, I₂, and I₃. Which of the following expresses the value of the total current I_T in the combined system?

A) I_T = (1/I₁ + 1/I₂ + 1/I₃)
B) I_T = I₁ = I₂ = I₃
C) I_T = I₁ + I₂ + I₃
D) I_T = (1/I₁ + 1/I₂ + 1/I₃) ^{- 1}

Question 49

Three resistors, each with resistance R₁, are in series in a circuit. They are replaced by one equivalent resistor, R. Comparing this resistor to the first resistor of the initial circuit, which of the following is true?

A) The voltage across R equals the voltage across R₁.
B) The current through R equals the current through R₁.
C) The power given off by R equals the power given off by R₁.
D) R is less than R₁.

Question 50

Which resistor is in series with resistor R?

A) R₃
B) R₄
C) R₁
D) R₂

Question 51

Three resistors connected in series each carry currents labeled I₁, I₂, and I₃. Which of the following expresses the value of the total current I_T in the system made up of the three resistors in series?

A) I_T = I₁ + I₂ + I₃
B) I_T = (1/I₁ + 1/I₂ + 1/I₃) ^{- 1}
C) I_T = (1/I₁ + 1/I₂ + 1/I₃)
D) I_T = I₁ = I₂ = I₃

Question 52

Three 3.0- $\Omega$ resistors are connected in parallel to a 12.0-V battery. What is the current in any one of the resistors?

A) 0.75 A
B) 12 A
C) 4.0 A
D) 1.3 A

Question 53

A solar panel measures 80 cm * 50 cm. In direct sunlight, the panel delivers 4.8 A at 15 V. If the intensity of sunlight is 1000 W/m², what is the efficiency of the solar panel in converting solar energy into electrical energy?

A) 12%
B) 24%
C) 18%
D) 6.0%

Question 54

Two resistors of values 6.0 and 12.0 $\Omega$ are connected in parallel. This combination in turn is hooked in series with an 8.0- $\Omega$ resistor and a 24-V battery. What is the current in the 12- $\Omega$ resistor?

A) 1.3 A
B) 4.0 A
C) 12 A
D) 0.67 A

Question 55

Three resistors connected in parallel have individual values of 4.0, 6.0, and 10.0 $\Omega$ , respectively. If this combination is connected in series with a 12-V battery and a 2.0- $\Omega$ resistor, what is the current in the 6.0- $\Omega$ resistor?

A) 0.98 A
B) 16 A
C) 0.59 A
D) 11 A

Question 56

Kirchhoff's rules are the junction rule and the loop rule. Which of the following statements is true?

A) The junction rule is based on the conservation of charge, and the loop rule is based on the conservation of energy.
B) The junction rule is based on the conservation of energy, and the loop rule is based on the conservation of charge.
C) Both rules are based on the conservation of charge.
D) Both rules are based on the conservation of energy.

Question 57

Three resistors connected in parallel have the individual voltages labeled $\Delta$ V₁, $\Delta$ V₂, and $\Delta$ V₃, respectively. Which of the following expresses the total voltage $\Delta$ V_T across the three resistors when connected in this manner?

A) " $\Delta$ V_T = (1/ $\Delta$ V₁ + 1/ $\Delta$ V₂ + 1/ $\Delta$ V₃)"
B) " $\Delta$ V_T = $\Delta$ V₁ + $\Delta$ V₂ + $\Delta$ V₃"
C) " $\Delta$ V_T = (1/ $\Delta$ V₁ + 1/ $\Delta$ V₂ + 1/ $\Delta$ V₃) ^{- 1}"
D) " $\Delta$ V_T = $\Delta$ V₁ = $\Delta$ V₂ = $\Delta$ V₃"

Question 58

When a 24.0- $\Omega$ resistor is connected across a 12.0-V battery, a current of 410 mA flows. What is the resulting terminal voltage of the battery?

A) 11.6 V
B) 9.8 V
C) 0.4 V
D) 12.0 V

Question 59

Three resistors connected in series have individual voltages labeled $\Delta$ V₁, $\Delta$ V₂, and $\Delta$ V₃, respectively. Which of the following expresses the value of the total voltage $\Delta$ V_T taken over the three resistors together?

A) " $\Delta$ V_T = (1/ $\Delta$ V₁ + 1/ $\Delta$ V₂ + 1/ $\Delta$ V₃)"
B) " $\Delta$ V_T = $\Delta$ V₁ = $\Delta$ V₂ = $\Delta$ V₃"
C) " $\Delta$ V_T = (1/ $\Delta$ V₁ + 1/ $\Delta$ V₂ + 1/ $\Delta$ V₃) ^{- 1}"
D) " $\Delta$ V_T = $\Delta$ V₁ + $\Delta$ V₂ + $\Delta$ V₃"

Question 60

Four 8.0- $\Omega$ resistors are connected in parallel. What is their equivalent resistance?

A) 4.0 $\Omega$
B) 0.50 $\Omega$
C) 2.0 $\Omega$
D) 32 $\Omega$

Question 61

If R₁ < R₂ < R₃, and if these resistors are connected in parallel in a circuit, which one has the highest current?

A) R₂
B) R₁
C) All have the same current.
D) R₃

Question 62

If I₁ goes to the right through R₁, I₂ goes to the right through R₂, and I₃ goes to the left through R₃, what is the resulting equation resulting from applying Kirchhoff's junction rule at point b?

A) I₁ - I₂ - I₃ = 0
B) I₁ - I₂ + I₃ = 0
C) I₁ + I₂ + I₃ = 0
D) I₁ + I₂ - I₃ = 0

Question 63

What is the potential difference between points a and b?

A) 24 V
B) 6 V
C) 8 V
D) 12 V

Question 64

If $\varepsilon$ = 9.0 V, what is the current in the 30- $\Omega$ resistor?

A) 0.30 A
B) 0.26 A
C) 0.10 A
D) 0.20 A

Question 65

Three resistors, each with resistance R₁, are in parallel in a circuit. They are replaced by one equivalent resistor, R. Compare this resistor to the first resistor of the initial circuit. Which of the following statements is true?

A) The current through R equals the current through R₁.
B) R is greater than R₁.
C) The power given off by R equals the power given off by R₁.
D) The voltage across R equals the voltage across R₁.

Question 66

Resistors of values 6.0 $\Omega$ , 4.0 $\Omega$ , 10.0 $\Omega$ and 7.0 $\Omega$ are combined as shown. What is the equivalent resistance for this combination?

A) 2.3 $\Omega$
B) 27 $\Omega$
C) 10.7 $\Omega$
D) 3.0 $\Omega$

Question 67

If I₁ goes to the right through R₁, I₂ goes to the right through R₂, and I₃ goes to the left through R₃, what is the resulting equation resulting from applying Kirchhoff's loop rule for a clockwise loop around the perimeter of the circuit?

A) 8.0 V - I₁R₁ + I₃R₃ = 0
B) 8.0 V - I₁R₁ - I₃R₃ = 0
C) 8.0 V + I₁R₁ + I₃R₃ = 0
D) -8.0 V - I₁R₁ + I₃R₃ = 0

Question 68

How much current is flowing in the 2- $\Omega$ resistor?

A) 0.8 A
B) 2.4 A
C) 1.6 A
D) 2.0 A

Question 69

Consider the circuit shown in the figure. What power is dissipated by the top 5- $\Omega$ resistor?

A) 14 W
B) 112 W
C) 17 W
D) 52 W

Question 70

What is the current through the 6- $\Omega$ resistor?

A) 1.0 A
B) 1.5A
C) 0.50 A
D) 2.0 A

Question 71

What is the current flowing through the 8- $\Omega$ resistor?

A) 6 A
B) 4 A
C) 2 A
D) 1 A

Question 72

Five resistors each have resistance R. Three of the resistors are connected in series and this combination is then connected in parallel with the two other resistors which have been connected in series with each other. What is the equivalent resistance for this arrangement?

A)
B)
C)
D)

Question 73

In the circuit segment shown if I = 8.0 mA and Q = 75 µC, what is the potential difference, V_A - V_B?

A) "-35 V"
B) "+15 V"
C) "-15 V"
D) "+35 V"

Question 74

Resistors of values 8.0 $\Omega$ , 12.0 $\Omega$ , and 24.0 $\Omega$ are connected in parallel across a fresh battery. Which resistor dissipates the least power?

A) the 24.0- $\Omega$ resistor
B) All dissipate the same power when in parallel.
C) the 12.0- $\Omega$ resistor
D) the 8.0- $\Omega$ resistor

Question 75

A battery has an internal resistance . Connecting a wire of negligible resistance between the terminals of the battery draws the maximum current from this battery. If instead a resistor is connected between the terminals, a smaller current is produced. What value resistor placed across the terminals would result in the current produced to be half of ?

A)
B)
C)
D)

Question 76

What is the equivalent resistance for these 3.00- $\Omega$ resistors?

A) 2.25 $\Omega$
B) 3.00 $\Omega$
C) 1.33 $\Omega$
D) 7.50 $\Omega$

Question 77

If I = 1.0 mA and the potential difference, V_A - V_B = +30 V in the circuit segment shown, determine the charge and polarity of the capacitor.

A) 1.0 mC, left plate is positive
B) 3.5 mC, right plate is positive
C) 3.5 mC, left plate is positive
D) 1.0 mC, right plate is positive

Question 78

If $\varepsilon$ = 20 V, at what rate is thermal energy being generated in the 40- $\Omega$ resistor?

A) 26 W
B) 1.6 W
C) 3.3 W
D) 15 W

Question 79

Four 1.5-volt AA batteries in series power a transistor radio. If the batteries hold a total charge of 440 C, how long will they last if the radio has a resistance of 200 $\Omega$ ?

A) 4.1 h
B) 2.2 h
C) 1.1 h
D) 13 h

Question 80

What is Kirchhoff's 1st equation for this junction?

A) I₁ + I₂ + I₃ = 0
B) I₂ = I₁+ I₂
C) I₃ = I₁ + I₂
D) I₁ = I₂ + I₃