Question 1

In schematic diagrams, currents are indicated using arrows.What do the arrows indicate?

Accepted Answer

A) the direction of motion of the electrons 
B) the direction of the current vector 
C) the direction of motion of the charge carriers 
D) the direction that positive charge carriers would move 
E) nothing; they are just a convenient drawing tool 
A) the direction of motion of the electrons 
B) the direction of the current vector 
C) the direction of motion of the charge carriers 
D) the direction that positive charge carriers would move 
E) nothing; they are just a convenient drawing tool

Question 2

Conductivity is:

Accepted Answer

A) the same as resistivity, it is just more convenient to use for good conductors 
B) expressed in $\Omega$-1 
C) equal to 1/resistance 
D) expressed in ($\Omega$.m)-1  
E) not a meaningful quantity for an insulator 
A) the same as resistivity, it is just more convenient to use for good conductors 
B) expressed in $\Omega$-1 
C) equal to 1/resistance 
D) expressed in ($\Omega$.m)-1  
E) not a meaningful quantity for an insulator

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 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 5

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 6

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 7

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 8

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 9

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 10

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

Question 11

Five cylindrical wires are made of the same material.Their lengths and radii are   Rank the wires according to their resistances, least to greatest.

Accepted Answer

A) 1, 2, 3, 4, 5 
B) 5, 4, 3, 2, 1 
C) 1 and 2 tie, then 5, 3, 4 
D) 1, 3, 4, 2, 5 
E) 1, 2, 4, 3, 5 
A) 1, 2, 3, 4, 5 
B) 5, 4, 3, 2, 1 
C) 1 and 2 tie, then 5, 3, 4 
D) 1, 3, 4, 2, 5 
E) 1, 2, 4, 3, 5

Question 12

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) 2.0 A 
C) 3.5 A 
D) 500 A 
E) 2100 A 
A) 0.83 A 
B) 2.0 A 
C) 3.5 A 
D) 500 A 
E) 2100 A

Question 13

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 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

Exam 26: Current and Resistance

In schematic diagrams, currents are indicated using arrows.What do the arrows indicate?

Conductivity 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 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?

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

Current in a conductor is normally due to:

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

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

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

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:

Five cylindrical wires are made of the same material.Their lengths and radii are Rank the wires according to their resistances, least to greatest.

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:

Energy may be measured in:

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:

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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:

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: