Physics

Problem

At a junction, a current of

1.80\,\text{A}

flows toward the point through one wire. Three other wires carry currents labeled

I_1

I_2

, and

I_3

. Currents

I_1

and

I_2

are directed away from the junction with magnitudes

0.75\,\text{A}

and

0.65\,\text{A}

, respectively. Current

I_3

has an unknown magnitude and direction. Which of the following statements about

I_3

is correct? a)

I_3 = 1.05\,\text{A}

directed away from the junction b)

I_3 = 0.40\,\text{A}

directed away from the junction c)

I_3 = 3.20\,\text{A}

directed away from the junction d)

I_3 = 0.40\,\text{A}

directed toward the junction

Intuitive explanation

This problem tests Kirchhoff's Current Law, which states that the total current flowing into a junction must equal the total current flowing out—charge can't accumulate at a point. Set up an equation where all currents flowing in are positive and all flowing out are negative (or vice versa), then solve for the unknown $I_3$ . The sign of your answer will tell you whether $I_3$ flows toward or away from the junction.

Intuitive explanation

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