# drift velocity

Prelecture Concept Question 25.01

Part A

Which of the following statements are true?

v

dv

4 dv

d/2v

2 dv

d/4v

Both cables carry the same current density.

The electrons have the same drift velocity in both cables.

The current in the thin cable is four times as great as the current in the thick cable.

The same current flows through both cables.

The current in the thin cable is twice as great as the current in the thick cable.

11/30/2018 HW4

https://session.masteringphysics.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=6872436 3/8

Check all that apply.

ANSWER:

Prelecture Concept Question 25.05

Part A

Consider two copper wires with the same cross-sectional area. Wire A is twice as long as wire B. How do the resistivities and resistances of the two wires compare?

Check all that apply.

ANSWER:

Prelecture Concept Question 25.09

Part A

A circuit maintains a constant resistance. If the current in the circuit is doubled, what is the effect on the power dissipated by the circuit?

ANSWER:

A battery does work on electric charges to bring them to a position of higher electric potential energy so that they can flow through a circuit to a lower potential energy.

The potential difference between the terminals of a battery, when no current flows to an external circuit, is referred to as the terminal voltage.

The internal resistance of a battery decreases with decreasing temperature.

A battery is a device that produces electricity by transforming chemical energy into electrical energy.

Wire A has twice the resistance of wire B.

Wire B has twice the resistance of wire A.

Wire A and wire B have the same resistance.

Wire A and wire B have the same resistivity.

Wire B has twice the resistivity of wire A.

Wire A has twice the resistivity of wire B.

11/30/2018 HW4

https://session.masteringphysics.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=6872436 4/8

Problem 25.16

Part A

The resistivity of gold is 2.44×10-8 Ω•m at room temperature. A gold wire that is 1.4 mm in diameter and 39 cm long carries a current of 950 mA. What is the electric field in the wire?

ANSWER:

Problem 25.24

Part A

A Nichrome wire is used as a heating element in a toaster. From the moment the toaster is first turned on to the moment the wire reaches it maximum temperature, the current in the wire drops by 20.0% from its initial value. What is the temperature change in the wire? The temperature coefficient of resistivity for Nichrome is 0.000400 (°C)-1.

ANSWER:

The power dissipated is reduced by a factor of 2.

The power dissipated remains constant.

The power dissipated is doubled.

The power dissipated is reduced by a factor of 4.

The power dissipated is quadrupled.

3.8×10−3 V/m

1.2×10−2 V/m

1.5×10−2 V/m

1.9×10−2 V/m

3.8×10−2 V/m

11/30/2018 HW4

https://session.masteringphysics.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=6872436 5/8

Problem 25.26

Part A

A piece of wire 41.5 cm long carries a current I when a voltage V is applied across its ends at a temperature of 0°C. If the resistivity of the material of which the wire is made varies with temperature as shown in the graph in the figure, what length of the same diameter wire is needed so that the same current flows when the same voltage is applied at temperature 400°C?

ANSWER:

Problem 25.29

Part A

When a voltage difference is applied to a piece of metal wire, a 4-mA current flows through it. If this metal wire is now replaced with a silver wire having twice the diameter of the original wire, how much current will flow through the silver wire? The lengths of both wires are the same, and the voltage difference remains unchanged. (The resistivity of the original metal is 1.68 × 10-8 Ω · m, and the resistivity of silver is 1.59 × 10-8 Ω · m.)

ANSWER:

625°C

200°C

300°C

400°C

500°C

cm

11/30/2018 HW4

https://session.masteringphysics.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=6872436 6/8

Problem 25.38

Part A

The voltage and power ratings of a particular light bulb, which are its normal operating values, are 110 V and 60 W. Assume the resistance of the filament of the bulb is constant and is independent of operating conditions. If the light bulb is operated with a current that is 50% of the current rating of the bulb, what is the actual power drawn by the bulb?

ANSWER:

Problem 25.44