Question 1

For an ohmic resistor, resistance is the proportionality constant for:
A) potential difference and electric field
B) current and electric field
C) current and length
D) current and cross-sectional area
E) current and potential difference

Accepted Answer

Ohm's Law states that the current through an ohmic resistor is directly proportional to the potential difference across it. The constant of proportionality is resistance. Therefore, resistance is the proportionality constant for current and potential difference.

Question 2

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 1 V
C) has a resistance of 2.5$\Omega$at 2 V
D) has a resistance of 25 $\Omega$ at 2 V
E) does not have a resistance

Accepted Answer

We can use the formula for Ohm's Law: 
V = IR

For the first measurement, when V = 2 V and I = 4 A: 
2 = 4R 
R = 0.5 Ω

For the second measurement, when V = 4 V and I = 10 A: 
4 = 10R 
R = 0.4 Ω

Since the resistance changes with the applied voltage, this sample does not obey Ohm's Law. However, we can use the average resistance between the two measurements: 
R = (0.5 Ω + 0.4 Ω)/2 = 0.45 Ω

Therefore, the sample has a resistance of 0.45 Ω at 1 V (since resistance is defined as the ratio of voltage to current). The closest choice is B, which states that the sample has a resistance of 0.5 Ω at 1 V.

Question 3

A student kept her 60-watt, 120-volt study lamp turned on from 2:00 PM until 2:00 AM. How many coulombs of charge went through it?
A) 150
B) 3,600
C) 7,200
D) 18,000
E) 21,600

Accepted Answer

The answer of A student kept her 60-watt, 120-volt study...

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 directly proportional to the electric field in the sample. This relationship is described by Ohm's law, which states that the current through a conductor is directly proportional to the voltage applied across it, and inversely proportional to its resistance. Resistance and electric field are related through the equation E = IR, where E is the electric field, I is the current, and R is the resistance. Therefore, the electron drift velocity (which is related to the current) is directly proportional to the electric field. The cross-sectional area and length of the sample, as well as the mass of an electron, do not affect the electron drift velocity in an ohmic substance.

Question 5

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

Question 6

If the potential difference across a resistor is doubled:
A) only the current is doubled
B) only the current is halved
C) only the resistance is doubled
D) only the resistance is halved
E) both the current and resistance are doubled

Accepted Answer

According to Ohm's law, V=IR, where V is the potential difference across the resistor, I is the current flowing through the resistor and R is the resistance of the resistor. If the potential difference is doubled while keeping the resistance constant, then the current will double as well. This can be seen from the formula as follows: If V is doubled, then I=V/R must also be doubled to maintain the same value of R. Therefore, only the current is doubled.

Question 7

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 resistivity.

Question 8

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...

Question 9

Two conductors are made of the same material and have the same length. Conductor A is a solid wire of diameter 1 m. Conductor B is a hollow tube of inside diameter 1 m and outside diameter 2 m. The ratio of their resistance, R_A/R_B, is: A) 1 B) C) 2 D) 3 E) 4

Accepted Answer

The answer of Two conductors are made of the same...

Question 10

A current of 0.5 ampere exists in a 60-ohm lamp. The applied potential difference is:
A) 15 V
B) 30 V
C) 60 V
D) 120 V
E) none of these

Accepted Answer

According to Ohm's law, V=IR, where V is the potential difference, I is the current, and R is the resistance. Plugging in the given values, we get:
V=0.5A x 60Ω = 30V
Therefore, the applied potential difference is 30 V.

Question 11

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: 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

Accepted Answer

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

Question 12

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

Accepted Answer

We can use the formula for power dissipation in a resistor:

P = V^2 / R

where P is the power in watts, V is the voltage across the resistor in volts, and R is the resistance in ohms.

We can rearrange this formula to solve for R and find the resistance of the given resistor:

R = V^2 / P

When the resistor is connected to a 3 V potential difference and dissipating 0.5 W, we have:

R = (3 V)^2 / 0.5 W = 18 ohms

Now we can use this resistance to find the power dissipated when the resistor is connected to a 1 V potential difference:

P = V^2 / R = (1 V)^2 / 18 ohms = 0.056 W

Therefore, the answer is D) 0.056 W.

Question 13

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.

Question 14

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

Accepted Answer

The answer of You wish to triple the rate of...

Question 15

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-sectionalarea 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 16

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 17

A flat iron is marked "120 volt, 600 watt". In normal use, the current in it is:
A) 2 A
B) 4 A
C) 5 A
D) 7.2 A
E) 0.2 A

Accepted Answer

The answer of A flat iron is marked "120 volt,...

Question 18

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 19

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 20

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

Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. This means that the current-voltage relationship should be a straight line passing through the origin. Graph II is the only graph that shows a linear relationship between current and voltage, therefore, it best represents the current-voltage relationship for a device that obeys Ohm's law.

Quiz 26: Current and Resistance

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

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 student kept her 60-watt, 120-volt study lamp turned on from 2:00 PM until 2:00 AM. How many coulombs of charge went through it?

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

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:

If the potential difference across a resistor is doubled:

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

Conductivity is:

Two conductors are made of the same material and have the same length. Conductor A is a solid wire of diameter 1 m. Conductor B is a hollow tube of inside diameter 1 m and outside diameter 2 m. The ratio of their resistance, RA/RB, is:

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

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:

Energy may be measured in:

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

For an ohmic substance, the resistivity depends on:

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

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

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

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

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

Two conductors are made of the same material and have the same length. Conductor A is a solid wire of diameter 1 m. Conductor B is a hollow tube of inside diameter 1 m and outside diameter 2 m. The ratio of their resistance, R_A/R_B, is:

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: