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Section 10.6 The Junction Rule
Exercises Activities
1. Shown below is part of a circuit where two wires combine into one wire.
Figure 10.6.1. Two wires meet at a junction. Which of the following do you think describes the current in the third wire? Explain your reasoning.
\(\displaystyle I_3 = I_1 + I_2\)
\(\displaystyle I_3 = I_1 \times I_2\)
\(\displaystyle I_3 = I_1 - I_2\)
\(\displaystyle \frac{1}{I_3} = \frac{1}{I_1} + \frac{1}{I_2}\)
\(I_3 = \) the bigger of \(I_1\) and \(I_2\)
I can’t figure out \(I_3\)
Principle 10.6.2 . The Junction Rule.
The Junction Rule tells us that at a junction, the sum of the incoming currents must equal the sum of the outgoing currents:
\begin{equation*}
\sum I_{\mathrm{in}} = \sum I_{\mathrm{out}}
\end{equation*}
The Junction Rule is based on conservation of charge. Along with the Loop Rule, it forms a basis for analyzing all circuits. Together, the two rules are sometimes known as Kirchhoff’s Laws.
2. One of your friends builds a circuit and measures a negative current through one of the light bulbs in their circuit. What do you think the negative means for current?
