The directed flow of free electrons (or charge) is called the electric current. The electric current may be classified into three main types:

1. Steady current (DC Current)
2. Varying current
3. Alternating current (AC Current)

Read: What are Current and Voltage?

Steady current (DC Current)

The first type of electric current we are going to discuss in the steady current (DC Current).

Steady current or dc current is the current whose magnitude does not change with time. It is constant with time.

The figure shows the graph between steady current and time. The value of current remains the same as the time changes.

The current provided by a battery is almost a steady current (d.c.).

Varying Current

When the magnitude of current changes with time, it is called a varying current.

The figure shows the graph between varying current and time. Note that the value of current varies with time.

Alternating Current

An alternating current is another type of electric current whose magnitude changes continuously with time and direction changes periodically.

Due to technical and economic reasons, we produce alternating currents that have sine waveform (or cosine waveform) as shown in the figure.

It is called alternating current because current flows in alternate directions in the circuit, i.e., from 0 to T/2 second (T is the time period of the wave) in one direction and from T/2 to T second in the opposite direction.

The current provided by an AC generator is alternating current that has sine (or cosine) waveform.