  # Understanding Voltage & Current In most types of electrical equipment, the current in a circuit is proportional to the voltage across that circuit.

For example:

• If a voltage across a circuit is lowered, then the current flowing in that circuit will be reduced.
• If a voltage across a circuit is raised, then the current flowing in that circuit will be increased.

Alternating Current (AC)

Alternating current is where the current in a circuit flows in both directions, changing its direction of current flow at a specific rate. In Australian power supply systems this is 50 times per second or referred to as 50 cycles or 50 hertz.

Direct Current (DC)

Direct current is where the current flows in one direction only. With direct current there is a positive and negative terminal between which a current will usually flow in one direction. This form of electricity is usually supplied from batteries, generators or converted from an alternating current source.

Complete circuit rule
For a current to flow there must be a complete circuit, from the source, through a conductor and returning to the source.

Charging current

There is a type of current flow that does not follow the complete circuit rule. When voltage is applied across a circuit to raise the voltage level, this requires a charging current. Charging current is proportional to the capacitance of the item across which a voltage has been applied and may show up as a fairly substantial current even though it is open at one end. 