A long straight conductor carries a time-dependent current described by I(t)= cases…

PHYSICS · Single correct · A Level · Physics · Electricity · Electricity

Problem

A long straight conductor carries a time-dependent current described by

I(t)=\begin{cases} +3\,\text{A} & 0\le t<2\,\text{s}\\ -3\,\text{A} & 2\,\text{s}\le t<4\,\text{s} \end{cases}

Which statement about the net charge that passes through the conductor during the entire 4 s interval is most accurate? (a) The net charge is

+6\,\text{C}

because the current is

+3\,\text{A}

for

2\,\text{s}

. (b) The net charge is

-6\,\text{C}

because the current is

-3\,\text{A}

for the last

2\,\text{s}

. (c) The net charge is

0\,\text{C}

because equal amounts of positive and negative charge flow in opposite directions. (d) The net charge is

12\,\text{C}

because the magnitudes of the two current segments add.