The voltage of the power supply is called the power supply voltage or electromotive force.

The power supply voltage that does the work of making current flow is called the electromotive force.

When the direction of the flow of current and  the size of the current are fixed, we call the electricity direct current (DC). A circuit in which direct current flows is called a direct current (DC) circuit. A power supply that sends out direct current, such as a battery, is called a DC power supply.

The direction of flow and size of the current sent from the electric power company to a home changes cyclically. This kind of electricity is called alternating current (AC), and a circuit in which alternating current flows is called an alternating current (AC) circuit. The size of AC voltage at any given time is called the instantaneous voltage, and the largest value among the instantaneous voltages is called the peak voltage. The size of the AC voltage that will perform the same amount of work as a DC voltage is called the effective voltage.

The direction of the current alternates between clockwise and counterclockwise.

Conductance, in contrast to resistance, is a measure indicating the ease of the flow of current and is measured in siemens. Conductivity is the reciprocal of resistivity, and it is measured in siemens per meter. (The siemens is an inverse ohm; it is also sometimes called a mho).

When there are multiple resistances in a circuit, we can consider them as a single effective resistance. The method of connecting resistances in a line is called a series connection. We calculate the value of the effective resistance in a series connection by totaling the individual resistance values. The other basic method of connecting resistances is called a parallel connection. At this time, the value of the effective resistance can be obtained by calculating the reciprocal of the sum of the reciprocals of each resistance.

The electric appliances that we use in our homes are connected in parallel to a power supply.