Question 1

A wire with a length of 150 m and a radius of 0.15 mm carries a current with a uniform current density of 2.8 *107 A/m2. The current is:

Accepted Answer

A)  0.63 A 
B)  2.0 A 
C)  5.9 A 
D)  300 A 
E)  26000 A 
A)  0.63 A 
B)  2.0 A 
C)  5.9 A 
D)  300 A 
E)  26000 A B

Question 2

You wish to triple the rate of energy dissipation in a heating device. To do this you could triple:

Accepted Answer

A)  the potential difference keeping the resistance the same 
B)  the current keeping the resistance the same 
C)  the resistance keeping the potential difference the same 
D)  the resistance keeping the current the same 
E)  both the potential difference and current 
A)  the potential difference keeping the resistance the same 
B)  the current keeping the resistance the same 
C)  the resistance keeping the potential difference the same 
D)  the resistance keeping the current the same 
E)  both the potential difference and current D

Question 3

A 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 wire is:

Accepted Answer

A)  2 * 10-6  $\Omega$ .m 
B)  8 * 10-6  $\Omega$ .m 
C)  1 * 10-7  $\Omega$ .m 
D)  4 * 10-7  $\Omega$ .m 
E)  5 *10-7  $\Omega$ .m 
A)  2 * 10-6  $\Omega$ .m 
B)  8 * 10-6  $\Omega$ .m 
C)  1 * 10-7  $\Omega$ .m 
D)  4 * 10-7  $\Omega$ .m 
E)  5 *10-7  $\Omega$ .m E

Question 4

The mechanical equivalent of heat is 1 cal = 4.18 J. The specific heat of water is 1 cal/g·K, and its mass is 1 g/cm3. An electric immersion water heater, rated at 400 W, should heat a liter of water from 10$\degree$C to 30$\degree$C in about:

Accepted Answer

A)  12 s 
B)  50 s 
C)  3.5 min 
D)  15 min 
E)  45 min 
A)  12 s 
B)  50 s 
C)  3.5 min 
D)  15 min 
E)  45 min

Question 5

A car battery is rated at 80 A.h. An ampere-hour is a unit of:

Accepted Answer

A)  power 
B)  energy 
C)  current 
D)  charge 
E)  force 
A)  power 
B)  energy 
C)  current 
D)  charge 
E)  force

Question 6

A 1.5-V battery is connected to a circuit and puts out a current of 0.45 A. How much power is the battery putting out?

Accepted Answer

A)  0.30 W 
B)  0.68 W 
C)  3.3 W 
D)  5.0 W 
E)  7.4 W 
A)  0.30 W 
B)  0.68 W 
C)  3.3 W 
D)  5.0 W 
E)  7.4 W

Question 7

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 8

This figure shows a junction. What is true of the currents?

Accepted Answer

A)  i1 = i0 + i2 
B)  i2= i0 + i1 
C)  i0 = i1 - i2 
D)  i1 = i0 - i2 
E)  i0 = i2- i1 
A)  i1 = i0 + i2 
B)  i2= i0 + i1 
C)  i0 = i1 - i2 
D)  i1 = i0 - i2 
E)  i0 = i2- i1

Question 9

A 60-watt light bulb carries a current of 0.5 ampere. The total charge passing through it in one hour is:

Accepted Answer

A)  3600 C 
B)  3000 C 
C)  2400 C 
D)  1800 C 
E)  120 C 
A)  3600 C 
B)  3000 C 
C)  2400 C 
D)  1800 C 
E)  120 C

Question 10

Compared to a conductor, a semiconductor

Accepted Answer

A)  has larger conductivity 
B)  has smaller resistivity 
C)  has a larger charge carrier density 
D)  has a negative temperature coefficient of resistivity 
E)  has zero resistivity 
A)  has larger conductivity 
B)  has smaller resistivity 
C)  has a larger charge carrier density 
D)  has a negative temperature coefficient of resistivity 
E)  has zero resistivity

Question 11

For an ohmic resistor, resistance is the proportionality constant for:

Accepted Answer

A)  potential difference and electric field 
B)  current density and electric field 
C)  current and length 
D)  current and cross-sectional area 
E)  current and potential difference 
A)  potential difference and electric field 
B)  current density and electric field 
C)  current and length 
D)  current and cross-sectional area 
E)  current and potential difference

Question 12

Two wires made of different materials have the same uniform current density. They carry the same current only if:

Accepted Answer

A)  their lengths are the same 
B)  their cross-sectional areas are the same 
C)  both their lengths and cross-sectional areas are the same 
D)  the potential differences across them are the same 
E)  the electric fields in them are the same 
A)  their lengths are the same 
B)  their cross-sectional areas are the same 
C)  both their lengths and cross-sectional areas are the same 
D)  the potential differences across them are the same 
E)  the electric fields in them are the same

Question 13

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 14

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 15

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 16

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

Question 17

Current in a conductor is normally due to:

Accepted Answer

A)  the collective motion of all electrons in the conductor 
B)  the thermal motion of the conduction electrons 
C)  the drift motion of the conduction electrons due to electric fields 
D)  the drift motion of both electrons and positrons 
E)  the drift motion of both electrons and protons 
A)  the collective motion of all electrons in the conductor 
B)  the thermal motion of the conduction electrons 
C)  the drift motion of the conduction electrons due to electric fields 
D)  the drift motion of both electrons and positrons 
E)  the drift motion of both electrons and protons

Question 18

Which of the following graphs best represents the current-voltage relationship for a device that obeys Ohm's law?

Accepted Answer

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

Question 19

An iron is marked "120 volt, 600 watt". In normal use, the current in it is:

Accepted Answer

A)  0.2 A 
B)  2 A 
C)  4 A 
D)  5 A 
E)  7.2 A 
A)  0.2 A 
B)  2 A 
C)  4 A 
D)  5 A 
E)  7.2 A

Question 20

A wire has an electric field of 6.2 V/m and carries a current density of 2.4 x 108 A/m2. What is its resistivity?

Accepted Answer

A)  6.7 x 10-10  $\Omega$ .m 
B)  1.5 x 10-8  $\Omega$ .m 
C)  2.6 x 10-8  $\Omega$ .m 
D)  3.9 x 107  $\Omega$ .m 
E)  1.5 x 109  $\Omega$ .m 
A)  6.7 x 10-10  $\Omega$ .m 
B)  1.5 x 10-8  $\Omega$ .m 
C)  2.6 x 10-8  $\Omega$ .m 
D)  3.9 x 107  $\Omega$ .m 
E)  1.5 x 109  $\Omega$ .m

Exam 26: Current and Resistance

A wire with a length of 150 m and a radius of 0.15 mm carries a current with a uniform current density of 2.8 *107 A/m2. The current is:

You wish to triple the rate of energy dissipation in a heating device. To do this you could triple:

A 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 wire is:

The mechanical equivalent of heat is 1 cal = 4.18 J. The specific heat of water is 1 cal/g·K, and its mass is 1 g/cm3. An electric immersion water heater, rated at 400 W, should heat a liter of water from 10 °\degree° C to 30 °\degree° C in about:

A car battery is rated at 80 A.h. An ampere-hour is a unit of:

A 1.5-V battery is connected to a circuit and puts out a current of 0.45 A. How much power is the battery putting out?

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

This figure shows a junction. What is true of the currents?

A 60-watt light bulb carries a current of 0.5 ampere. The total charge passing through it in one hour is:

Compared to a conductor, a semiconductor

For an ohmic resistor, resistance is the proportionality constant for:

Two wires made of different materials have the same uniform current density. They carry the same current only if:

Current has units:

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:

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

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

Current in a conductor is normally due to:

Which of the following graphs best represents the current-voltage relationship for a device that obeys Ohm's law?

An iron is marked "120 volt, 600 watt". In normal use, the current in it is:

A wire has an electric field of 6.2 V/m and carries a current density of 2.4 x 108 A/m2. What is its resistivity?

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A wire with a length of 150 m and a radius of 0.15 mm carries a current with a uniform current density of 2.8 *10⁷A/m². The current is:

A 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 wire is:

The mechanical equivalent of heat is 1 cal = 4.18 J. The specific heat of water is 1 cal/g·K, and its mass is 1 g/cm³. An electric immersion water heater, rated at 400 W, should heat a liter of water from 10 $\degree$ C to 30 $\degree$ C in about:

A wire has an electric field of 6.2 V/m and carries a current density of 2.4 x 10⁸ A/m². What is its resistivity?