This text is meant to accompany class discussions. It is not everything there is to know about the basics of electricity. It is meant as a  prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations (click here.)

If you change the voltage through a piece of electronics, such as a wire, while measuring the current through the wire you may get a graph like the one below.

Georg Simon Ohm noticed this relationship and called the relationship "Ohm's Law." In this graph The voltage divided by the current gives a constant slope. This slope is called the resistance. This means that

Where ΔV is the difference in voltage.

Any device that behaves like the graph above (with a straight line) is called an ohmic device. Many electrical components in today's electronics do not follow Ohm's law. But everything we will study does follow Ohms law. Examples of ohmic devices would be a wire, incandescent light bulb, electric stove heating element or a resistor. Electronic appliances like music players, computers, telephones, etc are NOT ohmic devices.

The flow of charges out of a battery is constant like the flow of water in a river. If this flow is measured over time, then is would constant.This constant flow or current is called a direct current. "d.c." for short.

Typically d.c. sources come from batteries.

However, there are other d.c. sources. Like the power supplies in computers and a.c. adapters. (But some cheaper a.c. adapters have a current with a small wiggle.)

If the flow in a river in a river could travel back and forth, then some of the time the flow would go forwards and and then backwards. At times it would even stop for a moment. This type of current is called an alternating current because is direction alternates. As a function of time, it would look like this graph.

This type of current comes from a wall outlet.