Conservation of Charge and Energy

Conservation of charge

As charge flows through a circuit, it doesn’t get used or lost. This means that whatever charge flows into a junction will flow out again.

Why does the conservation of charge also apply to current?

Since current is rate of flow of charge, it follows that whatever current flows into a junction is the same as the current flowing out of it

Kirchhoff’s First Law

The total current entering a junction = the total current leaving it

Conservation of energy

Energy transferred to a charge is an emf, and energy transferred from a charge is potential difference

Kirchhoff’s Second Law

The total emf around a series circuit = the sum of the potential differences across each component

Kirchhoff’s Second Law in symbols

ε = ΣIR