Networks, Time and Fields
Kirchhoff's Laws
13 minStudent plan
The two conservation rules that let you analyse any circuit, however tangled: current at a node, voltage around a loop.
After this lesson you can
- Apply the current law at a node and the voltage law around a loop
- Set up the equations for a two-loop circuit
- Know which law to reach for and when
The current law: charge is conserved
At any junction, the current flowing in equals the current flowing out. Charge does not pile up at a node or vanish from one.
If 100 mA arrives at a junction and one branch carries 40 mA away, the other branch must carry 60 mA. Not roughly, exactly.
This is why a parallel network draws more total current than any single branch, and it is your first check when a measurement looks wrong. If your meter says 100 mA in and 70 mA out across both branches, you have either mismeasured or there is a path you have not accounted for. The law is never the thing that is wrong.
In the full lesson
- The current law: charge is conserved
- The voltage law: energy is conserved
- Using both together
This lesson comes with the Student plan. The first module of Physics for Engineers is free.