Question 1

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 2

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 3

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

Question 4

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 5

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 6

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 7

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

Question 8

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 9

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 10

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 11

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 12

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 13

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 14

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 15

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 16

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 17

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 18

The resistance of a rod does NOT depend on:

Accepted Answer

A) its temperature 
B) its material 
C) its length 
D) its conductivity 
E) shape of its (fixed)cross-sectional area 
A) its temperature 
B) its material 
C) its length 
D) its conductivity 
E) shape of its (fixed)cross-sectional area

Question 19

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 20

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

Exam 26: Current and Resistance

The units of resistivity are:

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

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

Current has units:

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

For an ohmic substance, the resistivity depends on:

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?

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

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

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

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

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

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

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

Compared to a conductor, a semiconductor

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

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

The resistance of a rod does NOT depend on:

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?

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:

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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?