Question 1

In a conductor carrying a current we expect the electron drift speed to be:

Accepted Answer

A)  much greater than the average electron speed 
B)  much less than the average electron speed 
C)  about the same as the average electron speed 
D)  less than the electron speed at low temperature and greater than the electron speed at high temperature 
E)  less than the electron speed at high temperature and greater than the electron speed at low temperature 
A)  much greater than the average electron speed 
B)  much less than the average electron speed 
C)  about the same as the average electron speed 
D)  less than the electron speed at low temperature and greater than the electron speed at high temperature 
E)  less than the electron speed at high temperature and greater than the electron speed at low temperature

Question 2

Of the following the copper conductor that has the least resistance is:

Accepted Answer

A)  thin, long and hot 
B)  thick, short and cool 
C)  thick, long and hot 
D)  thin, short and cool 
E)  thin, short and hot 
A)  thin, long and hot 
B)  thick, short and cool 
C)  thick, long and hot 
D)  thin, short and cool 
E)  thin, short and hot

Question 3

Copper contains 8.4 *1028 free electrons per cubic meter. A copper wire of cross-sectional area 7.4 * 10-7 m2 carries a current of 1 A. The electron drift speed is approximately:

Accepted Answer

A)  3* 108 m/s 
B)  103 m/s 
C)  1 m/s 
D)  10-4 m/s 
E)  10-23 m/s 
A)  3* 108 m/s 
B)  103 m/s 
C)  1 m/s 
D)  10-4 m/s 
E)  10-23 m/s

Question 4

A current of 0.5 ampere exists in a 60-ohm lamp. The applied potential difference is:

Accepted Answer

A)  15 V 
B)  30 V 
C)  60 V 
D)  120 V 
E)  none of these 
A)  15 V 
B)  30 V 
C)  60 V 
D)  120 V 
E)  none of these

Question 5

It is better to send 10,000 kW of electric power long distances at 10,000 V rather than at 220 V because:

Accepted Answer

A)  there is less heating in the transmission wires 
B)  the resistance of the wires is less at high voltages 
C)  more current is transmitted at high voltages 
D)  the insulation is more effective at high voltages 
E)  the iR drop along the wires is greater at high voltage 
A)  there is less heating in the transmission wires 
B)  the resistance of the wires is less at high voltages 
C)  more current is transmitted at high voltages 
D)  the insulation is more effective at high voltages 
E)  the iR drop along the wires is greater at high voltage

Question 6

For an ohmic substance the resistivity is the proportionality constant for:

Accepted Answer

A)  current and potential difference 
B)  current and electric field 
C)  current density and potential difference 
D)  current density and electric field 
E)  potential difference and electric field 
A)  current and potential difference 
B)  current and electric field 
C)  current density and potential difference 
D)  current density and electric field 
E)  potential difference and electric field

Question 7

Conduction electrons move to the right in a certain wire. This indicates that:

Accepted Answer

A)  the current density and electric field both point right 
B)  the current density and electric field both point left 
C)  the current density points right and the electric field points left 
D)  the current density points left and the electric field points right 
E)  the current density points left but the direction of the electric field is unknown 
A)  the current density and electric field both point right 
B)  the current density and electric field both point left 
C)  the current density points right and the electric field points left 
D)  the current density points left and the electric field points right 
E)  the current density points left but the direction of the electric field is unknown

Question 8

The rate at which electrical energy is used may be measured in:

Accepted Answer

A)  watt/second 
B)  watt·second 
C)  watt 
D)  joule·second 
E)  kilowatt·hour 
A)  watt/second 
B)  watt·second 
C)  watt 
D)  joule·second 
E)  kilowatt·hour

Question 9

For an ohmic substance, the resistivity depends on:

Accepted Answer

A)  the electric field 
B)  the potential difference 
C)  the current density 
D)  the electron mean free time 
E)  the cross-sectional area of the sample 
A)  the electric field 
B)  the potential difference 
C)  the current density 
D)  the electron mean free time 
E)  the cross-sectional area of the sample

Question 10

A student kept her 60-watt, 120-volt study lamp turned on from 2:00 PM until 2:00 AM. How much charge went through it?

Accepted Answer

A)  720 C 
B)  3,600 C 
C)  7,200 C 
D)  18,000 C 
E)  21,600 C 
A)  720 C 
B)  3,600 C 
C)  7,200 C 
D)  18,000 C 
E)  21,600 C

Question 11

A certain resistor dissipates 0.5 W when connected to a 3 V potential difference. When connected to a 1 V potential difference, this resistor will dissipate:

Accepted Answer

A)  0.056 W 
B)  0.167 W 
C)  0.50 W 
D)  1.5 W 
E)  none of these 
A)  0.056 W 
B)  0.167 W 
C)  0.50 W 
D)  1.5 W 
E)  none of these

Question 12

If the potential difference across a resistor is doubled:

Accepted Answer

A)  only the current is doubled 
B)  only the current is halved 
C)  only the resistance is doubled 
D)  only the resistance is halved 
E)  both the current and resistance are doubled 
A)  only the current is doubled 
B)  only the current is halved 
C)  only the resistance is doubled 
D)  only the resistance is halved 
E)  both the current and resistance are doubled

Question 13

Two substances are identical except that the electron mean free time for substance A is twice the electron mean free time for substance B. If the same electric field exists in both substances the electron drift speed in A is:

Accepted Answer

A)  the same as in B 
B)  twice that in B 
C)  half that in B 
D)  four times that in B 
E)  one fourth that in B 
A)  the same as in B 
B)  twice that in B 
C)  half that in B 
D)  four times that in B 
E)  one fourth that in B

Question 14

Energy may be measured in:

Accepted Answer

A)  kilowatt 
B)  joule·second 
C)  watt 
D)  watt·second 
E)  volt/ohm 
A)  kilowatt 
B)  joule·second 
C)  watt 
D)  watt·second 
E)  volt/ohm

Question 15

A certain sample carries a current of 4 A when the potential difference is 2 V and a current of 10 A when the potential difference is 4 V. This sample:

Accepted Answer

A)  obeys Ohm's law 
B)  has a resistance of 0.5  $\Omega$  at 2 V 
C)  has a resistance of 2  $\Omega$  at 2 V 
D)  has a resistance of 25 $\Omega$  at 2 V 
E)  does not have a resistance 
A)  obeys Ohm's law 
B)  has a resistance of 0.5  $\Omega$  at 2 V 
C)  has a resistance of 2  $\Omega$  at 2 V 
D)  has a resistance of 25 $\Omega$  at 2 V 
E)  does not have a resistance

Question 16

A certain wire has resistance R. Another wire, of the same material, has half the length and half the diameter of the first wire. The resistance of the second wire is:

Accepted Answer

A)  R/4 
B)  R/2 
C)  R 
D)  2R 
E)  4R 
A)  R/4 
B)  R/2 
C)  R 
D)  2R 
E)  4R

Question 17

The units of resistivity are:

Accepted Answer

A)  ohm 
B)  ohm·meter 
C)  ohm/meter 
D)  ohm/meter2 
E)  none of these 
A)  ohm 
B)  ohm·meter 
C)  ohm/meter 
D)  ohm/meter2 
E)  none of these

Question 18

For a cylindrical resistor made of ohmic material, the resistance does NOT depend on:

Accepted Answer

A)  the current 
B)  the length 
C)  the cross-sectional area 
D)  the resistivity 
E)  the electron drift velocity 
A)  the current 
B)  the length 
C)  the cross-sectional area 
D)  the resistivity 
E)  the electron drift velocity

Question 19

Two conductors are made of the same material and have the same length. Conductor A is a solid wire of diameter 1 m. Conductor B is a hollow tube of inside diameter 1 m and outside diameter 2 m. The ratio of their resistance, RA/RB, is:

Accepted Answer

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

Question 20

If is the current density and is a vector element of area then the integral over an area represents:

Accepted Answer

A)  the electric flux through the area 
B)  the average current density at the position of the area 
C)  the resistance of the area 
D)  the resistivity of the area 
E)  the current through the area 
A)  the electric flux through the area 
B)  the average current density at the position of the area 
C)  the resistance of the area 
D)  the resistivity of the area 
E)  the current through the area

Exam 26: Current and Resistance

In a conductor carrying a current we expect the electron drift speed to be:

Of the following the copper conductor that has the least resistance is:

Copper contains 8.4 *1028 free electrons per cubic meter. A copper wire of cross-sectional area 7.4 * 10-7 m2 carries a current of 1 A. The electron drift speed is approximately:

A current of 0.5 ampere exists in a 60-ohm lamp. The applied potential difference is:

It is better to send 10,000 kW of electric power long distances at 10,000 V rather than at 220 V because:

For an ohmic substance the resistivity is the proportionality constant for:

Conduction electrons move to the right in a certain wire. This indicates that:

The rate at which electrical energy is used may be measured in:

For an ohmic substance, the resistivity depends on:

A student kept her 60-watt, 120-volt study lamp turned on from 2:00 PM until 2:00 AM. How much charge went through it?

A certain resistor dissipates 0.5 W when connected to a 3 V potential difference. When connected to a 1 V potential difference, this resistor will dissipate:

If the potential difference across a resistor is doubled:

Two substances are identical except that the electron mean free time for substance A is twice the electron mean free time for substance B. If the same electric field exists in both substances the electron drift speed in A is:

Energy may be measured in:

A certain sample carries a current of 4 A when the potential difference is 2 V and a current of 10 A when the potential difference is 4 V. This sample:

A certain wire has resistance R. Another wire, of the same material, has half the length and half the diameter of the first wire. The resistance of the second wire is:

The units of resistivity are:

For a cylindrical resistor made of ohmic material, the resistance does NOT depend on:

Two conductors are made of the same material and have the same length. Conductor A is a solid wire of diameter 1 m. Conductor B is a hollow tube of inside diameter 1 m and outside diameter 2 m. The ratio of their resistance, RA/RB, is:

If is the current density and is a vector element of area then the integral over an area represents:

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Copper contains 8.4 10²⁸ free electrons per cubic meter. A copper wire of cross-sectional area 7.4 10^-7 m² carries a current of 1 A. The electron drift speed is approximately:

Two conductors are made of the same material and have the same length. Conductor A is a solid wire of diameter 1 m. Conductor B is a hollow tube of inside diameter 1 m and outside diameter 2 m. The ratio of their resistance, R_A/R_B, is: