Physics

Problem

A student assumes that current

I_3

leaves a junction and calculates

I_3=-0.70\,\text{A}

. Which of the following best explains the physical meaning of the negative sign? a) No current flows in branch 3 because a negative current value is not physically possible. b) The magnitude of the current is

0.70\,\text{A}

and it still leaves the junction in the assumed direction. c) A current of

0.70\,\text{A}

actually enters the junction rather than leaving as originally assumed. d) The negative sign means electrons, rather than positive charge, move away from the junction with

0.70\,\text{A}

of current, so the original direction is still correct.

Intuitive explanation

The negative sign tells you that your initial assumption about current direction was wrong. When you set up Kirchhoff's junction rule, you guessed that $I_3$ flows out of the junction, but the math revealed it actually flows in. The magnitude $0.70\,\text{A}$ is correct—only the direction needs to be flipped. This is a feature, not a bug: it's how the equations self-correct your assumption.

Intuitive explanation

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