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Kirchoff's 1st Law

A conservation of stuff law

Kirchoff's first law says that charges can't just disappear and they can't appear from nowhere.  So at every junction in a circuit the current going in must equal the current going out.

Try Why Do Astronauts Float by Julian Hamm

This law is often used in the junctions at parallel circuits but it also implies that the current must be the same all the way round a series circuit.

A caveat

Kirchoff's first law doesn't suggest any of the deeper physics of a circuit.  In particular it doesn't say that current splits at junctions, simply that the current into a junction must equal the current coming out.

back to Lesson 5: Voltage and Current