Deck 18: Electric Current and Circuits

Question 1

If 64 coulombs flow along a wire in 4.0 seconds,what is the average current?

A) 64 A
B) 32 A
C) 16 A
D) 4.0 A
E) none of these choices are correct

Answer 1

16 A

Question 2

A variable resistor has a voltage of 12.0 V placed across it.If the resistance is increased 20%,what happens to the current through it?

A) it increases 20%
B) it increases 25%
C) it decreases 20%
D) it decreases 25%
E) it decreases 17%

Answer 2

it decreases 17%

Question 3

A length of wire has a resistance of 18.0 $\Omega$ .When the wire is uniformly stretched to triple it original length,what resistance results?

A) 162 $\Omega$
B) 54.0 $\Omega$
C) 18.0 $\Omega$
D) 6.00 $\Omega$
E) 2.00 $\Omega$

Answer 3

162 $\Omega$

Question 4

A resistor has a resistance of 30 $\Omega$ at 20 $^{\circ}$ C.If the temperature coefficient is 4.5 $\times$ 10³ $^{\circ}$ C^-1,what is its resistance at 200 $^{\circ}$ C?

A) 24 $\Omega$
B) 27 $\Omega$
C) 48 $\Omega$
D) 54 $\Omega$
E) 57 $\Omega$

Question 5

One hundred meters of a certain type of wire has a resistance of 7.2 $\Omega$ .What is the resistance of 2.5 m of this wire?

A) 18 $\Omega$
B) 1.8 $\Omega$
C) 0.18 $\Omega$
D) 3.0 $\Omega$
E) 0.30 $\Omega$

Question 6

A 12.0 V battery is placed across a 4.00 $\Omega$ resistor.If the current through the resistor is 2.80 A,what is the internal resistance of the battery?

A) 0.200 $\Omega$
B) 0.290 $\Omega$
C) 4.29 $\Omega$
D) 3.71 $\Omega$
E) 0.800 $\Omega$

Question 7

When a current flows down a wire

A) electrons are moving in the direction of the current.
B) electrons are moving opposite the direction of the current.
C) protons are moving in the direction of the current.
D) protons are moving opposite the direction of the current.
E) both protons and electrons are moving in the direction of the current.

Question 8

A 2.50 A current is carried by a copper wire of radius 1.0 mm.If the density of conduction electrons is 8.0 $\times$ 10²⁸/m³,what is the drift velocity of the conduction electrons?

A) 3.0 $\times$ 10⁸ m/s
B) 3.2 $\times$ 10 ⁴ m/s
C) 1.6 $\times$ 10 ⁵ m/s
D) 6.2 $\times$ 10 ⁴ m/s
E) 6.2 $\times$ 10 ⁵ m/s

Question 9

Of the common battery sizes AAA,AA,C,and D,which provides the highest emf?

A) AAA
B) AA
C) C
D) D
E) all have the same emf

Question 10

One hundred meters of 2.00 mm diameter wire has a resistance of 0.532 $\Omega$ .What is the resistivity of the material from which the wire is made?

A) 1.59 $\times$ 10 ⁸ $\Omega$ m
B) 1.67 $\times$ 10 ⁸ $\Omega$ m
C) 2.35 $\times$ 10 ⁸ $\Omega$ m
D) 2.65 $\times$ 10 ⁸ $\Omega$ m
E) 5.40 $\times$ 10 ⁸ $\Omega$ ·m

Question 11

An ampere, A ,is equivalent to a

A) V/m.
B) V·C.
C) C/s.
D) C·s.
E) N/V.

Question 12

A 1.56-V battery has an internal resistance of 0.120 $\Omega$ .What is the maximum current that can be drawn from this battery?

A) infinite (or at least 1000's of amps)
B) 1.56 A
C) 0.190 A
D) 13.0 A
E) 7.50 A

Question 13

A length L₀ of wire has a resistance of 32.0 $\Omega$ .The wire is uniformly stretched to four times its original length,i.e.,4 L₀.If a length L₀ is now cut from the stretched wire,what is its resistance?

A) 512 $\Omega$
B) 128 $\Omega$
C) 32.0 $\Omega$
D) 8.00 $\Omega$
E) 2.00 $\Omega$

Question 14

The resistance of a wire increases 3.9% when the temperature of the wire is raised 100 $^{\circ}$ C.What is the temperature coefficient of resistivity of the wire material?

A) 3.9 $^{\circ}$ C^-1
B) 0.39 $^{\circ}$ C^-1
C) 0.039 $^{\circ}$ C^-1
D) 0.0039 $^{\circ}$ C^-1
E) 0.00039 $^{\circ}$ C^-1

Question 15

An ohm is equivalent to a(n)

A) volt/meter.
B) coulomb/volt.
C) ampere/coulomb.
D) volt/ampere.
E) ampere·coulomb.

Question 16

A potential difference of 12.4 V is placed across a 4.1 $\Omega$ resistor.What is the current in the resistor?

A) 51 A
B) 3.0 A
C) 0.33 A
D) 16A
E) 8.3 A

Question 17

Silver contains 5.8 $\times$ 10²⁸ conduction electrons per m³.How many conduction electrons are in a 1.0 m length of silver wire of diameter 2.6 mm?

A) 1.9 $\times$ 10⁵
B) 4.7 $\times$ 10⁴
C) 3.1 $\times$ 10²³
D) 1.2 $\times$ 10²⁴
E) 6.0 $\times$ 10²³

Question 18

Two copper wires,one double the diameter of the other,have the same current flowing through them.If the thinner wire has a drift velocity v₁,and the thicker wire has a drift velocity v₂,how do the drift velocities of the charge carriers compare?

A) v₁ = v₂
B) v₁ = 2 v₂
C) 2 v₁ = v₂
D) v₁ = 4 v₂
E) 4 v₁ = v₂

Question 19

Aluminum has a resistivity of 2.65 $\times$ 10⁸ $\Omega$ m.What is the resistance of 15 m of aluminum wire of cross-sectional area 1.0 mm²?

A) 1.6 $\Omega$
B) 0.40 $\Omega$
C) 0.13 $\Omega$
D) 1.3 $\times$ 10² $\Omega$
E) 56 $\Omega$

Question 20

If a 22 $\Omega$ resistor has a current of 2.0 A flowing through it,what is the potential difference across it?

A) 0.091 V
B) 44 V
C) 11 V
D) 24 V
E) 20 V

Question 21

The arrangement is composed of four 6.0 mF capacitors.What is the capacitance of the combination?

A) 24.0 mF
B) 4.5 mF
C) 8.0 mF
D) 9.0 mF
E) 12.5 mF

Question 22

A 6.0 $\Omega$ resistor and a 3.0 $\Omega$ resistor are connected in parallel to a 1.5 V battery of negligible internal resistance.What is the current in the 3.0 $\Omega$ resistor?

A) 2.0 A
B) 0.50 A
C) 0.25 A
D) 0.17 A
E) 0.75 A

Question 23

Capacitors of values 6.00 mF and 9.00 mF are connected in series to a 30.0 V power supply.What is the resulting charge on the 6.00 mF capacitor?

A) 180 mC
B) 270 mC
C) 90.0 mC
D) 108 mC
E) 200 mC

Question 24

If R₁ = 6.0 $\Omega$ , R₂ = 8.0 $\Omega$ , R₃ = 2.0 $\Omega$ , $\varepsilon$ ₁ = 4.0 V, and $\varepsilon$ ₂ = 14 V,what is the power supplied to the circuit by $\varepsilon$ ₁?

A) 4.0 W
B) 8.0 W
C) 12 W
D) 16 W
E) 20 W

Question 25

A 6.0 $\Omega$ resistor and a 3.0 $\Omega$ resistor are connected in series to a 1.5 V battery of negligible internal resistance.What is the current in the 3.0 $\Omega$ resistor?

A) 2.0 A
B) 0.50 A
C) 0.25 A
D) 0.17 A
E) 0.75 A

Question 26

What is the resistance of the combination of resistors?

A) 4.0 $\Omega$
B) 12 $\Omega$
C) 13 $\Omega$
D) 14 $\Omega$
E) 15 $\Omega$

Question 27

If R₁ = 6 $\Omega$ , R₂ = 8 $\Omega$ , R₃ = 2 $\Omega$ , $\varepsilon$ ₁ = 4 V, and $\varepsilon$ ₂ = 14 V, what is the current in R₂?

A) 1 A
B) 2 A
C) 3 A
D) 4 A
E) 5 A

Question 28

Capacitors of values 1.0 F, 2.0 F, 3.0 F, and 6.0 F are connected in series across a 12 V power supply.Which capacitor has the greatest charge on it?

A) the 1.0 F capacitor
B) the 2.0 F capacitor
C) the 3.0 F capacitor
D) the 6.0 F capacitor
E) they are all equal

Question 29

In the diagram,each resistor is 3 ohms and the battery is 9 volts.What is the current through the middle resistor?

A) 3 A to the right
B) 3 A to the left
C) 9 A to the right
D) 9 A to the left
E) 1 A to the left

Question 30

Four 12 $\Omega$ resistors are connected together.

A) 12 $\Omega$
B) 24 $\Omega$
C) 36 $\Omega$
D) 48 $\Omega$
E) 44 $\Omega$

Question 31

Capacitors of values 6.0 mF and 9.0 mF are connected in series to a 30.0 V power supply.What is the resulting potential difference across the 6.0 mF capacitor?

A) 30 V
B) 18 V
C) 12 V
D) 6.0 V
E) 3.0 V

Question 32

Four 12 $\Omega$ resistors are connected together.What is the least resistance that can be attained with these resistors?

A) 12 $\Omega$
B) 6.0 $\Omega$
C) 3.0 $\Omega$
D) 2.0 $\Omega$
E) 1.0 $\Omega$

Question 33

Four 12 $\Omega$ resistors are connected together.Which of the following resistances cannot be formed using all 4 resistors?

A) 48 $\Omega$
B) 9.0 $\Omega$
C) 12 $\Omega$
D) 60 $\Omega$
E) 20 $\Omega$

Question 34

In the diagram,if the current through R₁ is 5 A up and if the current through R₃ is 3 A up, what is the current in R₂?

A) 8 A up
B) 8 A down
C) 2 A up
D) 2 A down
E) more information is needed

Question 35

Capacitors of values 1.0 F, 2.0 F, 3.0 F, and 6.0 F are connected in series across a 12 V power supply.Which capacitor has the greatest potential difference across it?

A) the 1.0 F capacitor
B) the 2.0 F capacitor
C) the 3.0 F capacitor
D) the 6.0 F capacitor
E) they all are equal

Question 36

A three-cell flashlight has 3 batteries in series each with an emf of 1.5 V.If the bulb has a resistance of 50 $\Omega$ ,what current is flowing when the flashlight is operating? (Assume the internal resistance of the batteries is negligible.)

A) 30 mA
B) 10 mA
C) 27 mA
D) 90 mA
E) 11 A

Question 37

A 12.0 V battery is placed across a 4.00 $\Omega$ resistor.If the current through the resistor is 2.80 A,what is the terminal voltage of the battery?

A) 12.0 V
B) 12.8 V
C) 11.6 V
D) 11.2 V
E) 9.6 V

Question 38

Capacitors of values 6.0 mF and 9.0 mF are connected in series.What is the capacitance of the combination?

A) 15 mF
B) 7.5 mF
C) 3.0 mF
D) 3.6 mF
E) 54 mF

Question 39

A 12.0 V battery has an internal resistance of 0.080 $\Omega$ .If the battery supplies 100 A when connected to a starter motor,what is the resistance of the motor?

A) 0.080 $\Omega$
B) 0.20 $\Omega$
C) 0.0012 $\Omega$
D) 0.040 $\Omega$
E) 0.012 $\Omega$

Question 40

Wire A carries 4 A into a junction,wire B carries 5 A into the same junction,and another wire is connected to the junction.What is the current in this last wire?

A) 4 A away from the junction
B) 9 A away from the junction
C) 4 A into the junction
D) 9 A into the junction
E) 1 A away from the junction

Question 41

A variable resistor is connected to a constant voltage source.When the resistance is increased from 5.5 $\Omega$ to 9.3 $\Omega$ ,what happens to the power dissipated?

A) no change
B) a 35% decrease
C) a 41% decrease
D) a 59% decrease
E) a 69% decrease

Question 42

A capacitor is connected in series with a resistor and a switch.With the switch open,the capacitor is charged to 9.0 V.When the switch is closed,how long will it take for the voltage across the capacitor to drop to 6.0 V if the time constant of the circuit is 4.0 s?

A) 0.3 s
B) 1.2 s
C) 1.6 s
D) 2.7 s
E) 12 s

Question 43

When the voltage across a resistor is decreased by 50%,what happens to the power dissipated?

A) it increases by 50%
B) it decreases by 50%
C) it decreases by 25%
D) it decreases by 71%
E) it decreases by 75%

Question 44

A 1000 $\Omega$ resistor is in a circuit with 30.0 mA flowing through it.A voltmeter with internal resistance 1000 $\Omega$ is used to measure the voltage across the resistor.What is the reading from the voltmeter if 30.0 mA still flows in the circuit?

A) 30.0 V
B) 29.9 V
C) 27.0 V
D) 15.0 V
E) 3.00 V

Question 45

By how much does the current fall after the switch is closed in a series RC circuit when three time constants have elapsed?

A) 5.0%
B) 38%
C) 62%
D) 95%
E) 100% since after 2 time constants the current is 0

Question 46

A flashlight,which uses two 1.5 V batteries in series,is turned on for 2.0 minutes.If the current in the flashlight is 100 mA,what is the energy dissipated?

A) 12 J
B) 9.0 J
C) 72 J
D) 36 J
E) 18 J

Question 47

A series circuit consists of a 12.0 V source of emf,a 2.00 mF capacitor,a 1000 $\Omega$ resistor,and a switch.When the switch is closed,how long does it take for the current to reach one-tenth its maximum value?

A) 0.693 s
B) 2.30 s
C) 4.61 s
D) 9.00 s
E) 18.0 s

Question 48

Three resistors, R₁ = 9.0 $\Omega$ , R₂ = 3.0 $\Omega$ , and R₃ = 1.0 $\Omega$ , are connected in parallel to a 9.0 V battery.What is the power dissipated by the R₂?

A) 2.0 W
B) 3.0 W
C) 9.0 W
D) 27 W
E) 81 W

Question 49

Raising the current through a resistor from 8.50 A to 11.3 A increases the power by

A) 33.0%.
B) 77.0%.
C) 113%.
D) 157%.
E) 0% (no change).

Question 50

A series circuit consists of a 1.02 V source of emf, a 2.00 mF capacitor, a 1000 $\Omega$ resistor, and a switch.When the switch is closed, how long does it take for the current to reach one-half its maximum value?

A) 0.693 s
B) 1.39 s
C) 2.00 s
D) 1.69 s
E) 0.0250 s

Question 51

Copper has 8.5 $\times$ 10²⁸ current carrying electrons per m³. A copper wire of radius 0.15 mm carries a current of 17 mA.What is the average drift velocity for the electrons?

A) 2.7 $\times$ 10^-9 m/s
B) 56 $\times$ 10^-6 m/s
C) 18 $\times$ 10^-6 m/s
D) more information is needed for this calculation

Question 52

Three resistors, R₁ = 4 $\Omega$ , R₂ = 3.0 $\Omega$ , and R₃ = 2.0 $\Omega$ , are connected in series to a 9.0 V battery.What is the power dissipated by R₁?

A) 2.0 W
B) 4.0 W
C) 5.1 W
D) 9.0 W
E) 2.3 W

Question 53

A 2.0 $\Omega$ resistor is connected across a 6.0 V power supply.An ammeter with internal resistance of 1.0 $\Omega$ is used to measure the current in this circuit.What is the ammeter reading?

A) 4.0 A
B) 3.0 A
C) 2.0 A
D) 1.0 A
E) an ammeter with less resistance than the rest of the circuit will not produce a reading

Question 54

A good ammeter has ________ resistance and a good voltmeter has ________ resistance."Good" means that it affects the system being measured by very little.

A) low,low
B) low,high
C) high,high
D) high,low
E) medium,no

Question 55

In a series circuit consisting of a 12.0 emf,a 2.00 mF capacitor,a 1.00 k $\Omega$ resistor and a switch,what is the voltage across the capacitor at a time $\tau$ after the switch is closed?

A) .632 V
B) 6.32 V
C) 7.58 V
D) 8.65 V

Question 56

Three resistors, R₁ = 9.00 $\Omega$ , R₂ = 3.00 $\Omega$ , and R₃ = 1.00 $\Omega$ , are connected in parallel to a 9.00 V battery.What is the total power dissipated in the circuit?

A) 180 W
B) 117 W
C) 99.0 W
D) 80.1 W
E) 18.0 W

Question 57

The watt, W, is equivalent to which of the following?

A) A·V
B) C·J
C) C/J
D) A/V
E) V²/A

Question 58

A series circuit consists of a 12.0 V source of emf, a 2.00 mF capacitor,a 1000 $\Omega$ resistor, and a switch.What is the time constant for this circuit?

A) 10.0 s
B) 2.00 s
C) 0.693 s
D) 0.0825 s
E) 1.00 ms

Question 59

A wire of radius 0.15 mm is made of an unknown metal and carries a current of 8.4 mA.The drift velocity for electrons in the wire is measured to be 36 $\times$ 10^-6 m/s.What is the carrier density of the metal from which the wire is made?

A) 1.3 $\times$ 10²⁹ m^-3
B) 4.2 $\times$ 10²⁸ m^-3
C) need more information to do this calculation.
D) 4.2 $\times$ 10³⁰ m^-3

Question 60

Three resistors, R₁ = 4.0 $\Omega$ , R₂ = 3.0 $\Omega$ , and R₃ = 2.0 $\Omega$ , are connected in series to a 9.0 V battery.What is the total power dissipated by the circuit?

A) 2.0 W
B) 4.0 W
C) 5.1 W
D) 9.0 W
E) 20 W

Question 61

A carbon resistor is made of a cylinder of carbon,of diameter 7.4 mm.If the resistivity of carbon is 3.5 $\times$ 10^-5 $\Omega$ m and when placed in a circuit a potential difference of 0.15 V exists when 12 A flows across the resistor,what is the length of the cylinder?

A) 6.1 cm
B) 1.5 cm
C) 0.15 cm
D) 0.5 cm

Question 62

In an RC circuit with an initially uncharged capacitor,the time constant is the time that is required for the charge on the capacitor to reach what percentage of its final value?

A) 50%
B) 37%
C) 100%
D) 63%
E) 90%

Question 63

Two carbon cylinders have radii r and 2r and they both have length L.What is the resistance of the first if the resistance of the second is 12 $\Omega$ ?

A) 48 $\Omega$
B) 12 $\Omega$
C) 24 $\Omega$
D) 3 $\Omega$
E) 6 $\Omega$

Question 64

Two carbon cylinders have radii 2r and r and the first has length 2L,while the second has length L.What is the resistance of the first if the resistance of the second is 12 $\Omega$ ?

A) 48 $\Omega$
B) 6 $\Omega$
C) 12 $\Omega$
D) 24 $\Omega$

Question 65

A carbon resistor is made of a cylinder of carbon,of length 1.5 cm.If the resistivity of carbon is 3.5 $\times$ 10^-5 $\Omega$ m and when placed in a circuit a potential difference of 0.15 V exists when 12 A flows across the resistor,what is the radius of the cylinder?

A) 6.5 mm
B) 12 mm
C) 3.7 mm
D) 1.2 mm

Question 66

A bird can safely land on a bare high voltage power line because

A) If both feet are touching the bare wire,they are at the same potential - and therefore no current can flow between the feet and through the bird's body
B) Its internal resistance is very high,so very little current will flow
C) The line cannot deliver enough current to harm it
D) Its feet are good insulators,and therefore it is protected

Question 67

In an RC circuit with an initially uncharged capacitor,the time constant is the time that is required for the current through the resistor to reach what percentage of its final value?

A) 63%
B) 90%
C) 37%
D) 100%
E) 50%

Question 68

An electron beam contains 1.5 $\times$ 10¹⁷ electrons per m³ and is confined to circular region of diameter 0.025 mm.The electrons in the beam are extremely energetic,and travel at nearly the speed of light.What is the current in the beam?

A) 1.4 A
B) 3.5 mA
C) 350 mA
D) 14 mA

Question 69

A capacitor in an RC circuit is charged,storing energy 1.25 mJ.What is the time required to discharge this capacitor,as compared to the time required to discharge an identical capacitor in an identical RC circuit which has stored 2.5 mJ?

A) twice the time
B) half the time
C) the same time
D) the answer depends on the values of R and C.

Question 70

Copper has 8.5 $\times$ 10²⁸ current carrying electrons per m³.A copper wire carries a current of 17 mA,and the drift velocity of the electrons is measured to be 18 $\times$ 10^-6 m/s.What is the wire radius?

A) 0.15 mm
B) 0.27 mm
C) 2.7 mm
D) 1.5 mm