Chapter 20 - Electric Circuits

You have three resistors, each of which has a resistance R. By connecting all three together in various ways, which one or more of the following resistance values can you obtain? A. 3R B. (3/2)R C. R D. (2/3)R E. (1/3)R

A. , B., D., E.

Which of the following devices is used placed into a circuit to measure the current that passes through it? A. ammeter B. gaultmeter C. voltmeter D. diffractometer E. flowmeter

A. ammeter

Complete the following statement: The unit kilowatt · hour measures A. energy. B. power. C. potential drop. D. voltage. E. current.

A. energy.

Two identical resistors are connected in series across the terminals of an ideal battery with a voltage V and a current I flows through the circuit. If one of the resistors is removed from the circuit and the remaining one connected across the terminals of the battery, how much current would flow through the circuit? A. 4I B. 2I C. I D. I/2 E. I/4

B. 2I

How does the capacitance of two identical capacitors connected in series compare to that of one of the capacitors? A. The two capacitors connected in series have the same capacitance. B. The two capacitors connected in series have a larger capacitance. C. The two capacitors connected in series have a smaller capacitance.

C. The two capacitors connected in series have a smaller capacitance.

Two wires are made from the same material. One wire has a resistance of 0.10 Ω. The other wire is twice as long as the first wire and has a radius that is half as much. What is the resistance of the second wire? A. 0.20 Ω B. 0.10 Ω C. 0.050 Ω D. 0.80 Ω E. 0.40 Ω

D. Reasoning: Since both wires are made from the same material, the resistivity ? is the same for each. The resistance R is given by R=ρL/A (Equation 20.3), where L is the length and A is the cross-sectional area of the wire. With twice the length and one-half the radius (one-fourth the cross-sectional area), the second wire has L/A=2/(1/4)=8 times the resistance as the first wire.

For the circuit shown in the drawing, what is the voltage V1 across resistance R1? http://edugen.wileyplus.com/edugen/courses/crs7924/art/qb/qu/c20/c20_q_8.gif A. V1=((R1+R2)/R1)V B. V1=V C. V1=(R1/R2)V D. V1=(R1/(R1+R2))V E. V1=(R2/R1)V

D. V1=(R1/(R1+R2))V Reasoning: According to Ohm's law, the voltage across the resistance R1 is V1 = IR1. The two resistors are connected in series, and their equivalent resistance is, therefore, R1 + R2. According to Ohm's law, the current in the circuit is I=v/(R1+R2) Substituting this expression into the expression for V1 gives V1=(V/(R1+R2))R1

Complete the following statement: The sum of the magnitudes of the currents directed into a junction A. is divided equally among the number of lines directed out of the B. is less than the total current directed out of the junction. C. equals the current that is directed along one of the lines out of the junction. D. equals the current that is directed along one of the lines out of the junction. E. is greater than the total current directed out of the junction.

D. equals the current that is directed along one of the lines out of the junction.

Complete the following statement: The sum of the magnitudes of the currents directed into a junction A. is divided equally among the number of lines directed out of the junction. B. is less than the total current directed out of the junction. C. equals the current that is directed along one of the lines out of the junction D. equals the sum of the magnitudes of the currents directed out of the junction. E. is greater than the total current directed out of the junction.

D. equals the sum of the magnitudes of the currents directed out of the junction.

The drawings show a number of different possibilities for connecting an ammeter (AM) and a voltmeter (VM) to a circuit, in order to measure the current in and the voltage across the resistor labeled R2. Which one of the possibilities shows the correct connections? http://edugen.wileyplus.com/edugen/courses/crs7924/art/qb/qu/c20/c20_q_17.gif A. C B. D C. E D. B E. A

E. A Reasoning: The ammeter must be connected so that the current that flows through the resistor R2 also flows through the ammeter. The voltmeter must be connected across the resistor R2.

Three resistors, 50-Ω, 120-Ω, 180-Ω, are connected in series in a circuit. What is the equivalent resistance of this combination of resistors? A. 350 Ω B. 120 Ω C. 250 Ω D. 29 Ω E. 200 Ω

A. 350 Ω

Which one of the following graphs correctly represents Ohm's law, where V is the voltage and I is the current? http://edugen.wileyplus.com/edugen/courses/crs7924/art/qb/qu/c20/c20_q_2.gif A. C B. B C. D D. A

A. C Reasoning: Ohm's law states that the voltage V is directly proportional to the current I, according to V = IR, where R is the resistance. Thus, a plot of voltage versus current is a straight line that passes through the origin.

When an incandescent light bulb is turned on, a constant voltage is applied across the tungsten filament, which then becomes white hot. The temperature coefficient of resistivity for tungsten is a positive number. What happens to the power delivered to the bulb as the filament heats up? A. It decreases. B. It increases. C. It remains constant.

A. It decreases

How does the resistance of a copper wire change when both the length and diameter of the wire are doubled? A. It decreases by a factor of two. B. It increases by a factor of two. C. It decreases by a factor of four. D. It increases by a factor of four. E. It does not change.

A. It decreases by a factor of two.

Three capacitors are connected in parallel to a battery. How is the equivalent capacitance for this circuit determined? A. The equivalent capacitance is the sum of the three capacitances. B. The equivalent capacitance is the sum of the three capacitances divided by three. In other words, the equivalent capacitance is the average capacitance in the circuit. C. The potential drop across each capacitor is measured and multiplied by each capacitance before adding them together. D. A resistor is used to replace one capacitor at a time. Then, the current through the resistor is measured and used to determine the charge on each capacitor. The sum of the charges is then divided by the emf of the battery to find the equivalent capacitance. E. Unlike resistors, an equivalent capacitance cannot be found by any simple means.

A. The equivalent capacitance is the sum of the three capacitances.

The potential difference across the ends of a wire is doubled in magnitude. If Ohm's law is obeyed, which one of the following statements concerning the resistance of the wire is true? A. The resistance is not changed. B. The resistance is one half of its original value. C. The resistance is twice its original value. D. The resistance increases by a factor of four. E. The resistance decreases by a factor of four.

A. The resistance is not changed.

How does the capacitance of two identical capacitors connected in parallel compare to that of one of the capacitors? A. The two capacitors connected in series have a larger capacitance. B. The two capacitors connected in series have the same capacitance. C. The two capacitors connected in series have a smaller capacitance.

A. The two capacitors connected in series have a larger capacitance.

Each appliance individually dissipates the same average power as it would if the other two devices were not plugged into the outlet. A. When the two resistors are wired in parallel, the equivalent resistance is less than if they are wired in series. B. When the two resistors are wired in series, the equivalent resistance is less than if they are wired in parallel. C. When the two resistors are wired in series, the equivalent resistance is less than if they are wired in parallel. D. When the two resistors are wired in series, the equivalent resistance is less than if they are wired in parallel.

A. When the two resistors are wired in parallel, the equivalent resistance is less than if they are wired in series.

The type of current that flows through a refrigerator when it is plugged into a wall socket is which of the following? A. alternating B. direct C. depends on whether it is the U.S. or in Europe D. electromagnetic

A. alternating

Three capacitors are identical, each having a capacitance C. Two of them are connected in series. Then, this series combination is connected in parallel with the third capacitor. What is the equivalent capacitance of the entire connection? A. 3C B. 3/2C C. 1/2C D. 1/3C E. 2/3C

B. 3/2C Reasoning: The two capacitors in series have an equivalent capacitance CS that can be determined from Cs=(1/C) + (1/C), so that Cs=1/2C This capacitance is in parallel with a capacitance C, so that the total equivalent capacitance is Ceq=1/2C + C = 3/2C

When a light bulb is connected to a 4.5 V battery, a current of 0.12 A passes through the bulb filament. What is the resistance of the filament? A. 1.4 Ω B. 38 Ω C. 28 Ω D. 9.3 Ω E. 440 Ω

B. 38 Ω

A single resistor is connected across the terminals of a battery. Which one or more of the following changes in voltage and current leaves unchanged the electric power dissipated in the resistor? (A) Doubling the voltage and reducing the current by a factor of two. (B) Doubling the voltage and increasing the resistance by a factor of four. (C) Doubling the current and reducing the resistance by a factor of four. A. A, B B. A, B, C C. B D. B, C E. A

B. A, B, C Reasoning: Power P is the current I times the voltage V or P = IV (Equation 20.6a). However, since Ohm's law applies to a resistance R, the power is also P =I2R (Equation 20.6b) and P=V^2/R (Equation 20.6c). Therefore, all three of the changes specified leave the power unchanged.

In analyzing circuits in which resistors are wired partially in series and partially in parallel, which one of the following statements describes the preferred approach to take to determine the equivalent resistance in the circuit? A. Find the sum of all the resistors. This is the equivalent resistance for the circuit B. Break the circuit into smaller parts and find an equivalent resistance for each part. Then continue this process until all of the parts are added together correctly either in series or parallel until a single equivalent resistance is found. C. Add together all of the resistors in series, ignoring any wired in parallel as they do not significantly add to the equivalent resistance of the circuit. The sum of the resistors in series is the equivalent resistance. D. Add together all of the resistors in series, ignoring any wired in parallel as they do not significantly add to the equivalent resistance of the circuit. The sum of the resistors in series is the equivalent resistance.

B. Break the circuit into smaller parts and find an equivalent resistance for each part. Then continue this process until all of the parts are added together correctly either in series or parallel until a single equivalent resistance is found.

Three capacitors are connected in series to a battery. Which one of the following statements concerning this situation is true? A. The equivalent capacitance is less than the sum of the individual capacitances. B. The battery must move more charge when the capacitors are connected in series than when connected in parallel. C. An equivalent capacitance can be found for capacitors connected in series, but not when they are connected in parallel.

B. The battery must move more charge when the capacitors are connected in series than when connected in parallel.

In an ac circuit containing a generator and a resistance, the voltage fluctuates in a sinusoidal manner. How does the current in such a circuit behave? A. The current has a constant value with time. B. The current also varies in a similar sinusoidal manner. C. The current alternates, but it only has two values with time, +I and -I. D. Since electrons do not flow in such a circuit, the current is zero amperes.

B. The current also varies in a similar sinusoidal manner.

Two materials have different resistivities. Two wires of the same length are made, one from each of the materials. Is it possible for each wire to have the same resistance? A. Yes, if the material with the greater resistivity is used for a thinner wire. B. Yes, if the material with the greater resistivity is used for a thicker wire. C. It is not possible.

B. Yes, if the material with the greater resistivity is used for a thicker wire.

A cylindrical wire has a length of 2.80 m and a radius of 1.03 mm. It caries a current of 1.35 A, when a voltage of 0.0320 V is applied across the ends of the wire. From what material in Table 20.1 is the wire made? A. silver B. aluminum C. gold D. copper

B. aluminum

A car has two headlights, and their power is derived from the car's battery. The filament in one burns out, but the other headlight stays on. Are the headlights connected in series or in parallel? A. series B. parallel

B. parallel

Which one of the following choices is not one of Kirchoff?s rules? A. junction rule B. slide rule C. loop rule

B. slide rule

Complete the following statement: The electromotive force is A. the force that accelerates protons through a wire when a battery is connected to it. B. the maximum potential difference between the terminals of a battery. C. the maximum capacitance between the terminals of a battery. D. the maximum electric potential energy stored within a battery. E. the force that accelerates electrons through a wire when a battery is connected to it.

B. the maximum potential difference between the terminals of a battery.

A 75-W and a 50-W incandescent light bulbs are designed for use with the same voltage. What is the ratio of the resistance of the 75-W bulb to the resistance of the 50-W bulb? A. 2.3 B. 0.44 C. 0.67 D. 3.0 E. 1.5

C. 0.67

You have four resistors, each of which has a resistance R. It is possible to connect these four together so that the equivalent resistance of the combination is also R. How many ways can you do it? There is more than one way. A. 3 B. 4 C. 2

C. 2 Reasoning: There are two ways. One is to form two groups of two parallel resistors and then connect the groups in series. The other is to form two groups of two series resistors and then connect the groups in parallel.

An ac current has an rms value of 3.54 A. Determine the peak value of the current. A. 2.50 A B. 7.08 A C. 5.00 A D. 1.25 A E. 3.75 A

C. 5.00 A

A toaster is designed to operate with a voltage of 120 V, and a clothes dryer is designed to operate with a voltage of 240 V. Based solely on this information, which appliance uses more power? A. The toaster B. The dryer C. Insufficient information is given for an answer

C. Insufficient information is given for an answer

Which one of the following statements concerning resistance is true? A. The resistance of a semiconductor increases with temperature. B. Resistance is a property of resistors, but not conductors. C. The resistance of a metal wire changes with temperature. D. The resistance is the same for all samples of the same material. E. The resistance of a wire is inversely proportional to the length of the wire.

C. The resistance of a metal wire changes with temperature.

One end of resistor A is connected to the positive terminal of a battery and the other end is connected to resistor B. The opposite end of resistor B is connected to the negative terminal of the battery. If resistor A has resistance R and B has a resistance 2R, what is the equivalent resistance of this circuit? A. The current through each resistor is necessarily the same. B. The equivalent resistance for the resistors in the circuit is the sum of the individual resistances. C. The voltage across each resistor D. The equivalent resistance for the resistors in the circuit is the product of the individual resistances. E. The equivalent resistance for the resistors in the circuit is the average of the individual resistances.

C. The voltage across each resistor

Which of the following statements concerning resistors that are wired in parallel is true? A. The equivalent resistance for the resistors in the circuit is the sum of the individual resistances. B. The voltage across each resistor is necessarily the same. C. The voltage across each resistor is necessarily the same. D. The equivalent resistance for the resistors in the circuit is the average of the individual resistances.

C. The voltage across each resistor is necessarily the same.

The resistance of a resistor-capacitor combination is reduced to one-third of its initial value. What must be done to the capacitance, in order that the time constant of the circuit remains unchanged? A. Reduce the capacitance to one-third of its initial value. B. Reduce the capacitance to one-ninth of its initial value. C. Triple the capacitance. D. Do nothing, for the time constant does not depend on the resistance. E. Increase the capacitance by a factor of nine.

C. Triple the capacitance. Reasoning: The time constant is given by the product of the resistance and the capacitance. Therefore, when the resistance is reduced to one-third of its initial value, the capacitance must be tripled, in order that the time constant remains unchanged.

Complete the following statement: Around any closed-circuit loop, the sum of the potential drops A. must equal zero (like the sum of the potential rises). B. is the same potential drop as in any other loop . C. equals the sum of the potential rises. D. equals the emf of the battery. E. must increase with the addition of any resistor.

C. equals the sum of the potential rises.

Which one of the following terms describes the resistance that a battery or a generator has in a circuit? A. super resistance B. critical resistance C. internal resistance D. terminal resistance E. electroresistance

C. internal resistance

Which of the following quantities is equal to the time constant for a charging capacitor? A. the time it takes a capacitor to reach 37 % of its maximum charge B. the time it takes a capacitor to reach 50 % of its maximum charge C. the time it takes a capacitor to reach 63 % of its maximum charge D. the time it takes a capacitor to reach 75 % of its maximum charge E. the time it takes a capacitor to reach its maximum charge

C. the time it takes a capacitor to reach 63 % of its maximum charge

What effect, if any, does increasing the capacitance in an RC circuit have on the charging of the capacitor? A. The capacitance has no effect on the charging of the capacitor, which is determined by the emf of the battery and the circuit resistance. B. Increasing the capacitance causes the charging time to increase since the rate at which charges are moving to the capacitor increases. C. The charging time will decrease as the capacitance is increased because the rate at which charges are moving to the capacitor decreases. D. Increasing the capacitance increases the charging time since the capacitor can hold more charge. E. Increasing the capacitance decreases the charging time since the emf of the battery will be reduced.

D. Increasing the capacitance increases the charging time since the capacitor can hold more charge.

A television, satellite receiver, and a DVD player are plugged into the same wall electrical outlet at Nancy?s house. Which of the following statements concerning this situation is false when these appliances are being used? A. The same voltage is provided to each of the three appliances by the outlet. B. Each appliance draws the same current as it would if the other two devices were not plugged into the outlet. C. The equivalent resistance of the three devices is less than the sum of the individual resistances. D. The current drawn by each of the three devices is identical. E. Each appliance individually dissipates the same average power as it would if the other two devices were not plugged into the outlet.

D. The current drawn by each of the three devices is identical.

In circuit A the battery that supplies energy has twice as much voltage as the battery in circuit B. However, the current in circuit A is only one-half the current in circuit B. Circuit A presents ____________ the resistance to the current that circuit B does. A. one-half B. the same C. one-fourth D. four times E. twice

D. four times

Which of the following actions would significantly reduce the risk of fire when using an electric heater connected to a wall outlet using an extension cord? A. use a longer extension cord B. use an extension cord with larger-gauge wire C. use a shorter extension cord D. use an extension cord with smaller-gauge wires E. use an extension cord with three prongs on the end rather than two

D. use an extension cord with smaller-gauge wires

When does a charging capacitor stop charging? A. when the amount of charge on the two plates is equal B. when the potential difference across the plates of the capacitor is equal to zero volts C. when the amount of charge on the two plates is infinitely large D. when the potential difference across the plates of the capacitor is equal to the emf of the battery E. when all of the charge available in the circuit has been forced to collect on the plates of the capacitor

D. when the potential difference across the plates of the capacitor is equal to the emf of the battery

One end of resistor A is connected to the positive terminal of a battery and the other end is connected to resistor B. The opposite end of resistor B is connected to the negative terminal of the battery. If resistor A has resistance R and B has a resistance 2R, what is the equivalent resistance of this circuit? A. R B. 3R/2 C. 2R D. 2R/3 E. 3R

E. 3R

Which one of the following statements is not a characteristic of a voltmeter? A. The voltmeter measures the voltage between two points in a circuit. B. The voltmeter is designed to measure nearly the same voltage that is present when the meter is not connected. C. The voltmeter is not placed directly into a circuit. D. The voltmeter is designed to draw very little current from the circuit being measured. E. An ideal voltmeter has almost no resistance

E. An ideal voltmeter has almost no resistance

Which one of the following statements is not a characteristic of a voltmeter? A. The voltmeter measures the voltage between two points in a circuit. B. The voltmeter is designed to measure nearly the same voltage that is present when the meter is not connected. C. The voltmeter is not placed directly into a circuit. D. The voltmeter is designed to draw very little current from the circuit being measured. E. An ideal voltmeter has almost no resistance.

E. An ideal voltmeter has almost no resistance.

Which one of the following statements concerning resistors in series is true? A. The total current through the resistors is the sum of the current through each resistor. B. The rate at which charge flows through each resistor depends on its resistance. C. The voltage across each resistor is the same. D. The power dissipated by each resistor is the same. E. The current through each resistor is the same.

E. The current through each resistor is the same.

The fact that the sum of the currents entering any junction in an electric circuit must be equal to the sum of the currents leaving the junction is an expression of what principle? A. conservation of energy B. Heisenberg uncertainty principle C. conservation of momentum D. Archimedes' Principle E. conservation of charge

E. conservation of charge