Question 1

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

Accepted Answer

For an ohmic substance, the relationship between current density and electric field is linear, and the proportionality constant is the substance's resistivity.

Question 2

Which of the following graphs best represents the current-voltage relationship for a device that obeys Ohm's law? 
A)I
B)II
C)III
D)IV
E)V

Accepted Answer

The answer of Which of the following graphs best represents...

Question 3

Suppose the electric company charges 10 cents per kW.h.How much does it cost to use a 125 watt lamp 4 hours a day for 30 days?
A)$1.20
B)$1.50
C)$1.80
D)$7.20
E)none of these

Accepted Answer

The answer of Suppose the electric company charges 10 cents...

Question 4

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

Accepted Answer

The electron drift velocity in an ohmic substance is proportional to the electric field applied to the substance, according to Ohm's Law. Therefore, the correct choice is D - the electric field in the sample. The other choices are not directly or solely proportional to the electron drift velocity.

Question 5

Which of the following graphs best represents the current-voltage relationship of an incandescent light bulb? 
A)I
B)II
C)III
D)IV
E)V

Accepted Answer

The answer of Which of the following graphs best represents...

Question 6

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

Accepted Answer

According to Ohm's law, for an ohmic resistor, the current passing through the resistor is directly proportional to the potential difference applied across it. This proportionality constant is the resistance of the resistor, which is given by the equation R=V/I. Therefore, the resistance is the proportionality constant for current and potential difference.

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? 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

Accepted Answer

The resistivity (ρ) can be found using the equation ρ = E/J, where E is the electric field and J is the current density. Substituting the given values, ρ = 6.2/2.4x10^11 = 2.6x10^-8 Ωm. Therefore, the best choice is C.

Question 8

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:
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

Accepted Answer

The electron drift speed is directly proportional to the electron mean free time. Therefore, if the electron mean free time in substance A is twice that in substance B, the electron drift speed in A will be twice that in B.

Question 9

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: 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

Accepted Answer

The answer of A wire is 1 m long and...

Question 10

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

Accepted Answer

The answer of Five cylindrical wires are made of the...

Question 11

For a cylindrical resistor made of ohmic material, the resistance does NOT depend on:
A)the current
B)the length
C)the cross-sectional area
D)the resistivity
E)the electron drift velocity

Accepted Answer

The answer of For a cylindrical resistor made of ohmic...

Question 12

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)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

Accepted Answer

Using Ohm's law, we know that resistance (R) is equal to the ratio of the potential difference (V) and the current (I): R = V/I.

At 2V and 4A, we can calculate the resistance as R = 2V/4A = 0.5 Ω.

At 4V and 10A, we can calculate the resistance as R = 4V/10A = 0.4 Ω.

Since the resistance changes with different potential differences, the sample does not obey Ohm's law. However, we can find the resistance of the sample at a specific potential difference, which gives us a value of 0.5 Ω at 2V. Therefore, the best choice is B) has a resistance of 0.5 Ω at 2V.

Question 13

Conductivity is: 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

Accepted Answer

The answer of Conductivity is:
A)the same as resistivity, it is...

Question 14

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

Accepted Answer

The answer of A certain wire has resistance R.Another wire,...

Question 15

The rate at which electrical energy is used may be measured in:
A)watt/second
B)watt·second
C)watt
D)joule·second
E)kilowatt·hour

Accepted Answer

The answer of The rate at which electrical energy is...

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

Accepted Answer

The resistance $R$ of a cylindrical conductor (like a copper rod) is given by $R = \rho \frac{L}{A}$, where $\rho$ is the resistivity of the material, $L$ is the length, and $A$ is the cross-sectional area. When the rod is stretched to twice its original length without changing its volume, its cross-sectional area $A$ is halved (since volume $V = A \cdot L$ remains constant and $L$ is doubled). The new resistance $R'$ can be calculated as $R' = \rho \frac{2L}{A/2} = 4 \rho \frac{L}{A} = 4R$, indicating that the resistance becomes four times the original resistance.

Question 17

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

Accepted Answer

The thicker the conductor, the lower the resistance. The shorter the conductor, the lower the resistance. The cooler the conductor, the lower the resistance. Therefore, the best option is a thick, short and cool conductor.

Question 18

For an ohmic substance, the resistivity depends on:
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

Accepted Answer

The resistivity of an ohmic substance is influenced by the electron mean free time, as it affects how easily electrons can move through the material, thus impacting its resistance. Other options like electric field, potential difference, current density, and cross-sectional area affect resistance or current flow but do not directly affect the material's inherent resistivity.

Question 19

The resistance of a rod does NOT depend on:
A)its temperature
B)its material
C)its length
D)its conductivity
E)shape of its (fixed)cross-sectional area

Accepted Answer

The resistance of a rod depends on its temperature, material, length, and conductivity, but not on the shape of its (fixed) cross-sectional area, as long as the area remains constant. Resistance is primarily a function of material properties, dimensions, and temperature, but the shape of the cross-section does not affect resistance if the area is the same.

Question 20

Energy may be measured in:
A)kilowatt
B)joule·second
C)watt
D)watt·second
E)volt/ohm

Accepted Answer

Energy is measured in watt·seconds, among other units like joules. Kilowatts and watts are units of power, not energy. Volt/ohm is not a valid unit for energy; it simplifies to watts, which again, measure power. Joule·second is not a standard unit of energy; the joule alone is the correct unit for energy.

Quiz 26: Current and Resistance

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

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

Suppose the electric company charges 10 cents per kW.h.How much does it cost to use a 125 watt lamp 4 hours a day for 30 days?

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

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

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

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?

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:

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.

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

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:

Conductivity is:

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

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

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

For an ohmic substance, the resistivity depends on:

The resistance of a rod does NOT depend on:

Energy may be measured in:

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 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: