Chapter 26

Front 1

Consider positive and negative charges moving horizontally through the four regions shown in Figure . Rank the currents in these four regions, from lowest to highest.

1. (b), (c), (a), (d)

3. (c) = (b), (a), (d)

Back 1

1.

Front 2

Two conductors are made of the same material and have the same length. The ratio of their cross sectional areas is 2:1. What is the ratio of their resistances?

* d. 1:2

e. 1:4

Back 2

d.

Front 3

The ampere-hour is used to rate batteries. What quantity does this measure?

* d. Energy

e. Work

Back 3

B

Front 4

In which one of the following situations does a conventional electric current flow due north?

a) Protons in a beam are moving due south.

b) A water molecule is moving due north.

c) Electrons in a beam are moving due south.

d) Electrons in a wire connected to a battery are moving from south to north.

Back 4

C

Front 5

The battery capacity of a lithium ion battery in a digital music player is 750 mA-h. The manufacturer claims that the player can operate for eight hours if the battery is initially fully charged. Given this information, determine the number of electrons that flow through the player as you listen to your favorite songs for three hours.

a) 6.2 × 1018 electrons

b) 1.0 × 103 electrons

c) 2.4 × 109 electrons

d) 6.3 × 1021 electrons

e) 8.1 × 1028 electrons

Back 5

D

Front 6

When lightning strikes, the current flows from the ground upward to the clouds above. What is the direction of the electric field of the lightning?

a) upward

b) downward

c) perpendicular to the current at each location on the lightning bolt

d) parallel to the ground

Back 6

a

Front 7

Which one of the following statements concerning the electric field inside a conductor is true if electrons are moving from right to left in a conducting wire?

a) The electric field must be zero in this case.

b) The electric field is directed perpendicular to the direction the electrons are moving.

c) The electric field is directed toward the left.

d) The electric field is directed toward the right.

Back 7

D

Front 8

A copper wire is fabricated that has a gradually increasing diameter along its length as shown. If an electric current is moving through the wire, which quantities vary along the length of the wire?

a) current only

b) current and current density only

c) current density and electric field only

d) resistivity and current only

e) current, resistivity, current density, and electric field

Back 8

c

Front 9

The magnitude of the electric field within a conducting wire depends on which of the following quantities?

a) potential difference, wire diameter, wire length, and wire conductivity

b) potential difference and wire conductivity only

c) potential difference, wire length, and wire conductivity only

d) wire diameter, wire length, and wire conductivity only

e) The magnitude of the electric field inside the conductor is always zero.

Back 9

C.

Front 10

Wires A and B are identical, except that the length of wire A is one-half that of wire B. If the same potential difference is applied between the two ends of each wire, how does the electric field within wire A compare to that in wire B?

a) The electric field in wire A is one fourth that in wire B.

b) The electric field in wire A is one half that in wire B.

c) The electric field in wire A is the same as that in wire B.

d) The electric field in wire A is twice that in wire B.

e) The electric field in wire A is four times that in wire B.

Back 10

D

Front 11

A circuit contains a battery and a resistor of resistance R. For which one of the following combinations of current and voltage does R have the smallest value?

a) V = 9 V and i = 0.002 A

b) V = 12 V and i = 0.5 A

c) V = 1.5 V and i = 0.075 A

d) V = 6 V and i = 0.1 A

e) V = 4.5 V and i = 0.009 A

Back 11

C

Front 12

For which combination for the length L and radius r of a wire will the resistance have the smallest value?

a) L = 0.50 m and r = 0.03 m

b) L = 0.25 m and r = 0.08 m

c) L = 0.40 m and r = 0.2 m

d) L = 0.80 m and r = 0.1 m

e) L = 0.10 m and r = 0.05 m

Back 12

C

Front 13

The ends of a wire are connected to the terminals of a battery. For which of the following changes will the resulting current in the circuit have the largest value?

a) Replace the wire with one that has a larger resistivity.

b) Replace the wire with one that has a larger radius.

c) Replace the wire with one that has a longer length.

Back 13

B

Front 14

A voltage V is applied to a device of resistance R; and the current through the device is i. If the device obeys Ohm’s law, what will be the outcome if the voltage is increased to 2V?

a) The current will increase to 2i.

b) The current will decrease to i/2.

c) The resistance will increase to 2R.

d) The resistance will decrease to R/2.

e) Two or more of the above statements are correct.

Back 14

A

Front 15

In a certain circuit containing a battery and a resistor, Ohm’s law is obeyed. An instrument to measure the current in the circuit, an ammeter, is connected in between one of the terminals of the battery and one end of the resistor. The ammeter indicates that the current in the circuit is i. The battery is then removed and replaced with another battery. This time, the ammeter indicates the current is 2i. Which one of the following statements concerning the resistor is true?

a) When the second battery was placed in the circuit, the resistance increased to twice its initial value.

b) When the second battery was placed in the circuit, the resistance decreased to one half its initial value.

c) When the second battery was placed in the circuit, the resistance increased to four times its initial value.

d) When the second battery was placed in the circuit, the resistance increased to one fourth its initial value.

e) When the second battery was placed in the circuit, the resistance did not change.

Back 15

E

Front 16

A certain circuit contains a battery and a resistor. An instrument to measure the current in the circuit, an ammeter, is connected in between one of the terminals of the battery and one end of the resistor. The graph shows the current in the circuit as the voltage is increased. Which one of the following statements best describes the resistor in this circuit?

a) The resistor does not obey Ohm’s law.

b) The resistor obeys Ohm’s law for

voltages between zero and

twenty-five volts.

c) The resistor obeys Ohm’s law for

voltages between zero and thirty-five volts.

d) The resistor obeys Ohm’s law for

voltages between zero and forty volts.

e) The resistor obeys Ohm’s law for

voltages between thirty and forty volts.

Back 16

B

Front 17

The drift speed within a certain conductor is 0.10 mm/s. How many electrons move through a unit cross-sectional area in the circuit each second if the current is 2.5 A?

a) 2.5 × 104

b) 1.6 × 1015

c) 1.6 × 1023

d) 2.5 × 1022

e) 6.4 × 1028

Back 17

C

Front 18

A copper wire is fabricated that has a gradually increasing diameter along its length as shown. If an electric current is moving through the wire, how does the drift velocity of the electrons at point A compare with that at point B?

a) The drift velocity will be greater at point A than at point B.

b) The drift velocity will be the same at both points.

c) The drift velocity will be greater at point B than at point A.

Back 18

a

Front 19

An automatic coffee maker uses a resistive heating element to boil the 2.4 kg of water that was poured into it at 21 °C. The current delivered to the coffee pot is 8.5 A when it is plugged into a 120 V electrical outlet. If the specific heat capacity of water is 4186 J/kg▪C°, approximately how long does it take to boil all of the water?

a) 5 minutes

b) 8 minutes

c) 10 minutes

d) 13 minutes

e) 15 minutes

Back 19

D. - how did this work out?

Front 20

The insulated wiring in a house can safely carry a maximum current of 18 A. The electrical outlets in the house provide an alternating voltage of 120 V. A space heater when plugged into the outlet operates at an average power of 1500 W. How many space heaters can safely be plugged into a single electrical outlet and turned on for an extended period of time?

a) zero

b) one

c) two

d) three

e) four

Back 20

B.

Front 21

A portable CD player was recently introduced that has a “special power saving technology.” The manufacturer claims that with only two standard AA batteries (together: 3.0 V, 20 kJ energy storage) that the player can be played for about 25 hours. What is the approximate resistance in the CD player’s electrical circuitry?

a) 40 Ω

b) 0.010 Ω

c) 300 Ω

d) 1.5 Ω

e) 15 Ω

Back 21

A. - How?

Front 22

A wire is used as a heating element that has a resistance that is fairly independent of its temperature within its operating range. When a current i flows through the wire, the energy delivered by the heater each minute is E. For what amount of current will the energy delivered by the heater each minute be 4E?

a) 2i

b) 4i

c) 0.5i

d) 0.25i

e) 8i

Back 22

A