Electricity moves through a circuit according to the polarity, or charge, of the power source and the various loads in the circuit. The power source of a circuit has positively charged and negatively charged terminals. Electricity is the flow of electrons, which have a negative charge.
Electrical current travels from the negative terminal of the power supply, through the circuit and back into the positive terminal to repeat the cycle. Two types of electrical currents exist: AC and DC. AC stands for alternating current, which reverses polarity of the power source dozens of times per second to increase the output. It is used for household electricity and other applications requiring high voltages. DC stands for direct current, which flows only one way and is used for low-voltage applications, such as a car battery or a radio.
Some elements on a circuit that alter the flow of electricity are switches and diodes. Switches open and close the circuit. An open circuit is broken, whereas a closed circuit allows electricity to flow. Diodes, meanwhile, keep electricity flowing in only one direction, even on an AC circuit.
Circuits can be wired in series or parallel. Series circuits have a single path, whereas parallel circuits have multiple paths. Most practical applications use parallel circuits.