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Kirchhoff's current law
Intermediate
Currents into a junction sum to zero.
ΣI = 0At any junction, the sum of currents in equals the sum out: ΣI = 0, from conservation of charge.
3 A and 2 A in give 5 A out.
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In more detail
Kirchhoff's current law states that the total current entering a junction equals the total current leaving it. It follows from conservation of charge.
Real-world uses
- Analysing currents in branching circuits.
- Power distribution networks are analysed using Kirchhoff's current law.
- Electricians use Kirchhoff's current law to check that the current entering a junction equals the current leaving it.
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Frequently asked questions
Does it apply to any node?
Yes, at any junction in a circuit.
Why is it charge conservation?
Because charge cannot accumulate at a junction, so the total in equals the total out.
Why does the current law hold?
Charge cannot build up at a junction in a steady state, so what flows in must flow out.
Related topics in Current Electricity & Circuits
Electrical energy and cost · EMF and internal resistance · Cells in series and parallel · Kirchhoff's voltage law · Wheatstone bridge · Meter bridge