An avionics technician tests a direct-current (DC) instrument subsystem and measures a ste… — Armed Services Vocational Aptitude Battery (ASVAB)

An avionics technician tests a direct-current (DC) instrument subsystem and measures a steady current of $2.5\text{ amperes}$ through a supply conductor. Which of the following statements correctly describes the movement of electrical charge through this conductor?

A
The direction of electron drift continuously alternates back and forth across the conductor at a rate of $2.5\text{ cycles}$ per second.
A total charge of $2.5\text{ coulombs}$ passes a cross-section of the conductor each second, with electrons drifting from the negative terminal toward the positive terminal.Answer
C
A total charge of $2.5\text{ coulombs}$ passes a cross-section of the conductor each second, with electrons physically moving from the positive terminal toward the negative terminal.
D
An electromotive force of $2.5\text{ volts}$ is consumed every second to push static charges through the conductor without net transfer of charge.

Answer

A total charge of

2.5\text{ coulombs}

passes a cross-section of the conductor each second, with electrons drifting from the negative terminal toward the positive terminal.

One ampere is formally defined as one coulomb of electric charge passing a given point in a circuit per second (

I = Q/t

). For a steady current of

2.5\text{ amperes}

2.5\text{ coulombs}

of charge pass through the conductor each second. Furthermore, in solid metallic wires, current is carried by negatively charged electrons that physically drift away from the negative polarity terminal toward the positive polarity terminal.

Step-by-Step Solution

Define electric current in terms of fundamental electrical units

Current (

I

) is defined as the rate of charge flow:

I = \frac{Q}{t}

, where

1\text{ ampere} = 1\text{ coulomb per second}

. Therefore,

2.5\text{ A} = 2.5\text{ C/s}

Establishing the relationship between amperes and coulombs per second confirms the rate of charge transfer.

Determine the physical direction of charge carriers in a DC conductor

In solid metal conductors, charge carriers are negatively charged free electrons that are repelled by the negative power supply terminal and attracted to the positive terminal.

Identifying the electron flow model distinguishes physical charge motion from conventional current flow.

Key Concept

Definition of the ampere as coulombs per second and the direction of physical electron drift in DC circuits

Estimated Time:40s

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