Question 1

The mechanical equivalent of heat is 1 cal = 4.18 J. A heating coil, connected to a 120-V source, develops 60,000 calories in 10 minutes. The current in the coil is:

Accepted Answer

A)  0.83 A 
B)  2 A 
C)  3.5 A 
D)  20 A 
E)  50 A 
A)  0.83 A 
B)  2 A 
C)  3.5 A 
D)  20 A 
E)  50 A

Question 2

Current has units:

Accepted Answer

A)  kilowatt·hour 
B)  ampere 
C)  coulomb 
D)  volt 
E)  ohm 
A)  kilowatt·hour 
B)  ampere 
C)  coulomb 
D)  volt 
E)  ohm

Question 3

Current is a measure of:

Accepted Answer

A)  force that moves a charge past a point 
B)  resistance to the movement of a charge past a point 
C)  energy used to move a charge past a point 
D)  amount of charge that moves past a point per unit time 
E)  speed with which a charge moves past a point 
A)  force that moves a charge past a point 
B)  resistance to the movement of a charge past a point 
C)  energy used to move a charge past a point 
D)  amount of charge that moves past a point per unit time 
E)  speed with which a charge moves past a point

Question 4

Which one of the following quantities is correctly matched to its unit?

Accepted Answer

A)  power - kW·h 
B)  energy - kW 
C)  potential difference - J/C 
D)  current - A/s 
E)  resistance - V/C 
A)  power - kW·h 
B)  energy - kW 
C)  potential difference - J/C 
D)  current - A/s 
E)  resistance - V/C

Question 5

Which of the following graphs best represents the current-voltage relationship of an incandescent light bulb?

Accepted Answer

A)  I 
B)  II 
C)  III 
D)  IV 
E)  V 
A)  I 
B)  II 
C)  III 
D)  IV 
E)  V

Question 6

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 7

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 8

A current of 0.3 A is passed through a lamp for 2 minutes using a 6 V power supply. The energy dissipated by this lamp during the 2 minutes is:

Accepted Answer

A)  1.8 J 
B)  12 J 
C)  20 J 
D)  36 J 
E)  216 J 
A)  1.8 J 
B)  12 J 
C)  20 J 
D)  36 J 
E)  216 J

Question 9

The current density is the same in two wires. Wire A has twice the free electron concentration of wire B. The drift speed of electrons in A is:

Accepted Answer

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

Question 10

The current is zero in a conductor when no potential difference is applied because:

Accepted Answer

A)  the electrons are not moving 
B)  the electrons are not moving fast enough 
C)  for every electron with a given velocity there is another with a velocity of equal magnitude and opposite direction 
D)  equal numbers of electrons and protons are moving together 
E)  otherwise Ohm's law would not be valid 
A)  the electrons are not moving 
B)  the electrons are not moving fast enough 
C)  for every electron with a given velocity there is another with a velocity of equal magnitude and opposite direction 
D)  equal numbers of electrons and protons are moving together 
E)  otherwise Ohm's law would not be valid

Question 11

A certain x-ray tube requires a current of 7 mA at a voltage of 80 kV. The rate of energy dissipation (in watts) is:

Accepted Answer

A)  560 
B)  5600 
C)  26 
D)  11.4 
E)  87.5 
A)  560 
B)  5600 
C)  26 
D)  11.4 
E)  87.5

Question 12

You buy a "75 W" light bulb. The label means that:

Accepted Answer

A)  no matter how you use the bulb, the power will be 75 W 
B)  the bulb was filled with 75 W at the factory 
C)  the actual power dissipated will be much higher than 75 W since most of the power appears as heat 
D)  the bulb is expected to "burn out" after you use up its 75 watts 
E)  none of the above 
A)  no matter how you use the bulb, the power will be 75 W 
B)  the bulb was filled with 75 W at the factory 
C)  the actual power dissipated will be much higher than 75 W since most of the power appears as heat 
D)  the bulb is expected to "burn out" after you use up its 75 watts 
E)  none of the above

Question 13

For an ohmic substance, the electron drift velocity is proportional to:

Accepted Answer

A)  the cross-sectional area of the sample 
B)  the length of the sample 
C)  the mass of an electron 
D)  the electric field in the sample 
E)  none of the above 
A)  the cross-sectional area of the sample 
B)  the length of the sample 
C)  the mass of an electron 
D)  the electric field in the sample 
E)  none of the above

Question 14

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 15

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 16

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 17

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 18

A nichrome wire is 1 m long and 1 *10-6 m2 in cross-sectional area. When connected to a potential difference of 2 V, a current of 4 A exists in the wire. The resistivity of this nichrome is:

Accepted Answer

A)  10-7 $\Omega$. m 
B)  2 *10-7 $\Omega$ . m 
C)  4 *10-7 $\Omega$ . m 
D)  5 *10-7 $\Omega$ . m 
E)  8* 10-7 $\Omega$ . m 
A)  10-7 $\Omega$. m 
B)  2 *10-7 $\Omega$ . m 
C)  4 *10-7 $\Omega$ . m 
D)  5 *10-7 $\Omega$ . m 
E)  8* 10-7 $\Omega$ . m

Question 19

An 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)  0.5 W 
B)  0.167 W 
C)  1.5 W 
D)  0.056 W 
E)  none of these 
A)  0.5 W 
B)  0.167 W 
C)  1.5 W 
D)  0.056 W 
E)  none of these

Question 20

A cylindrical copper rod has resistance R. It is reformed to twice its original length with no change of volume. Its new resistance is:

Accepted Answer

A)  R 
B)  2R 
C)  4R 
D)  8R 
E)  R/2 
A)  R 
B)  2R 
C)  4R 
D)  8R 
E)  R/2

Exam 26: Current and Resistance

The mechanical equivalent of heat is 1 cal = 4.18 J. A heating coil, connected to a 120-V source, develops 60,000 calories in 10 minutes. The current in the coil is:

Current has units:

Current is a measure of:

Which one of the following quantities is correctly matched to its unit?

Which of the following graphs best represents the current-voltage relationship of an incandescent light bulb?

Energy may be measured in:

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

A current of 0.3 A is passed through a lamp for 2 minutes using a 6 V power supply. The energy dissipated by this lamp during the 2 minutes is:

The current density is the same in two wires. Wire A has twice the free electron concentration of wire B. The drift speed of electrons in A is:

The current is zero in a conductor when no potential difference is applied because:

A certain x-ray tube requires a current of 7 mA at a voltage of 80 kV. The rate of energy dissipation (in watts) is:

You buy a "75 W" light bulb. The label means that:

For an ohmic substance, the electron drift velocity is proportional to:

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

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

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:

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

A nichrome wire is 1 m long and 1 *10-6 m2 in cross-sectional area. When connected to a potential difference of 2 V, a current of 4 A exists in the wire. The resistivity of this nichrome is:

An 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:

A cylindrical copper rod has resistance R. It is reformed to twice its original length with no change of volume. Its new resistance is:

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A nichrome wire is 1 m long and 1 *10^-⁶ m² in cross-sectional area. When connected to a potential difference of 2 V, a current of 4 A exists in the wire. The resistivity of this nichrome is: