Physics

Problem

In an aluminium strip, the electron number density is

8.5\times10^{28}\,\text{m}^{-3}

. The strip has a cross-sectional area of

1.0\,\text{mm}^2

and the electrons acquire a drift velocity of

2.0\times10^{-4}\,\text{m\,s}^{-1}

. Calculate the current through the strip. a)

27\,\text{A}

0.27\,\text{A}

2.7\,\text{A}

1.3\,\text{A}

Intuitive explanation

Current is the flow of charge per unit time, and the key is connecting the microscopic motion of electrons (their drift velocity) to the macroscopic current we measure. Use the relationship $I = nAve$ , where $n$ is electron density, $A$ is cross-sectional area, $v$ is drift velocity, and $e$ is the elementary charge—this formula counts how many electrons pass through a cross-section each second and multiplies by the charge each carries.

Intuitive explanation

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