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# Introduction to a.c.

## Alternating current definition

Alternating current (a.c.) is a form of current that periodically changes direction in a circuit.

If a direct current flows through a metal wire, the electrons move from the negative to the positive pole.

In a.c., the poles switch rapidly. This means that the electrons also change directions when the poles switch. However, the total amount of movement and work done is the same.

In d.c., the electrons flow all the way around the circuit. In a.c., the electrons move only tiny distances back and forth.

A person gets equally exhausted from swimming $1000 \text{ m}$ in a lake or $20\times 25 \text{ m}$ back and forth ($1000 \text{ m}$ in total) in a pool.

Similarly, electrons flowing back and forth in an a.c. circuit can deliver the same amount of power as electrons flowing only in one direction.

The voltage also switches from positive to negative when the current changes direction.

Comparison of d.c. and a.c. voltages with the same average power output.