In a direct current (DC) circuit, an ammeter measures the rate of charge flow past a speci… — Armed Services Vocational Aptitude Battery (ASVAB)

In a direct current (DC) circuit, an ammeter measures the rate of charge flow past a specific point. If exactly $1.248 \times 10^{19}$ electrons flow past this point in $4\text{ seconds}$ , and $1\text{ Coulomb}$ is defined as approximately $6.24 \times 10^{18}$ electrons, which of the following correctly identifies the current magnitude and describes the standard convention for its flow direction relative to the actual electrons?

$0.5\text{ A}$ ; conventional current flows from positive to negative, opposite to the actual electron flow.Answer
B
$0.05\text{ A}$ ; conventional current flows from positive to negative, opposite to the actual electron flow.
C
$0.5\text{ A}$ ; conventional current flows from negative to positive, identical to the actual electron flow.
D
$5.0\text{ A}$ ; conventional current flows from negative to positive, identical to the actual electron flow.

Answer

The current is

0.5\text{ A}

, and conventional current is analyzed as flowing from positive to negative, which is opposite to the actual electron flow.

The total charge is found by dividing the number of electrons by the electrons per Coulomb:

1.248 \times 10^{19} / 6.24 \times 10^{18} = 2\text{ Coulombs}

. The current is the charge divided by time:

2\text{ C} / 4\text{ s} = 0.5\text{ A}

. Standard electrical convention dictates that current flows from positive to negative, which is physically opposite to the actual movement of negatively charged electrons.

Step-by-Step Solution

Convert the given number of electrons into Coulombs of charge.

1.248 \times 10^{19} \text{ electrons} / 6.24 \times 10^{18} \text{ electrons/C} = 2\text{ Coulombs}

Current is defined as the rate of charge flow in Coulombs per second, not electrons per second.

Calculate the current magnitude in Amperes.

I = Q / t = 2\text{ C} / 4\text{ s} = 0.5\text{ A}

One Ampere is equivalent to one Coulomb of charge passing a point in one second.

Determine the relationship between conventional current and actual electron flow.

Conventional current is directed positive to negative, opposite to actual electron flow (negative to positive).

Standard circuit analysis uses conventional current (positive charge flow), while solid conductors actually move negatively charged electrons.

Key Concept

Electrical Current Calculations and Flow Conventions

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