Direct current flows in only one direction in a circuit, from the negative terminal of the voltage source to the positive. A common source of direct current (DC) is a battery. The three most common types of batteries are dry cell (used in small devices like TV remotes), wet cell (used for cars), and deep-cycle (storage batteries used primarily for backup and emergency power).

Current is the rate of flow of electrons per unit time and is measured in amperes (A). A coulomb (C) is the quantity of electricity conveyed in one second by a current of one ampere.

A schematic is the proper name for a drawing of an electric or electronic circuit.

An electrical circuit is a path through which electricity flows. This path contains one or more components that create a load (something that is using electricity) and that load acts as resistance to the passage of electricity through the circuit. Electricity can only flow through a circuit when the path is closed and cannot flow through an open circuit.

A thermocouple is a temperature sensor that consists of two wires made from different conductors. The junction of these two wires produces a voltage based on the temperature difference between them and can be used like a switch to open or close the circuit at a designated temperature.