There are two common kinds of circuits, DC, or Direct Current, and AC, or Alternating Current. In a DC circuit, current always flows one direction. In an AC circuit, poles of the circuit are reversed in a regular repeating cycle. In the next part of the cycle, the second pole is more positive, and the first pole is more negative. Most of the circuits we'll talk about in this class will be DC circuits.
Voltage is a measure of the electrical energy of a circuit.
It is measured in Volts. Resistance is a measure of a material's ability to oppose the flow of electricity. It is measured in Ohms. These formulas are handy, since often you're given two pieces of information about a circuit or component and you need to figure out a third piece of information. Components Conductors are materials through which electrical current moves freely.