Atoms (the stuff that makes up stuff) have a nucleus; a hard center which determines the atom’s weight and properties. This nucleus is made of both positively charged protons and charge-less neutrons. Spinning around that nucleus at near the speed of light are clouds of electrons; particles with a negative charge. Normally the atoms have an identical number of electrons and protons, and because of this atoms typically have a net charge of 0. However, these electrons can be removed or added leaving the atom charged either charged positively or negatively, respectively.
Atoms don’t like to be charged however and they do their best to become neutral. Metals tend to allow their electron clouds to be modified easily, and when you add one electron to a metal atom’s cloud another one jumps out into a neighboring atom’s cloud. This bumps another electron out of that cloud and a chain reaction is put into place. An electric current is now formed in the conductor, and it will continue until a bumped electron hits a positively charged atom and fills the “hole” in that atom’s cloud. This flow from negative to positive is called electricity.
One electron can’t do much though, and atoms don’t stay charged for a long time. In order to create steady current a galvanic cell is needed. There are other ways of generating a current, but this is the simplest to explain. In their simplest form, a cell is made by submerging 2 different metals in an electrolyte solution, such as an acid. A chemical reaction takes place and an imbalance of electrons is created as the more electronegative metal reduces and steals electrons from (oxidizes) the other metal. This leaves the reducing metal with an excess of electrons, while the oxizing metal lacks electrons.
By connecting these two metals with a wire the electrons will flow from the negatively charged metal (anode) to the positively charged metal (cathode). Until the cathode is completely oxidized a steady current is generated in the wire; a current that can do work.
There is a problem though; one cell typically does not have a large electron imbalance, or voltage (V). Because of this the electrons don’t have much “push” or “pressure”. In the typical carbon-zinc or alkaline cell the potential is 1.5V, which really can’t do very much. To increase the voltage, cells can be connected end to end, negative to positive. This increases the electron imbalance [voltage] between the two ends of the string of cells, and increases the “pressure” of the electrons. This string is called a battery, a term derived from a battery of cannons. The more voltage you have the more pressure the electrons have, and when you have huge voltages electrons can actually jump right out of a wire, as can be seen by this video.
But wait, since voltage is “electrical pressure” then there must be a measurement of volume, shouldn’t there? Well there is, and the measure is called the Ampere (A). The ampere, or amp, is the volume of electrons that are flowing (current). The unit is equivalent to about 6,242,000,000,000,000,000 (an assload) electrons flowing past a point in one second. Different electrical appliances require different amperages, with the typical LED flashlight requiring 60 milliamps (0.06A), an iPod requiring about 400mA and a refrigerator requiring 10A. With more current more work can be done, since more electrons carry more energy than fewer electrons. As can be seen by this video of a roofing nail burning, when large currents flow quite a lot of “work” can be done.
But what do we use to measure work exactly? We measure work, or power in Watts. The watt measures the rate at which work is done, and the electrical watt is the work that one volt at one amp can do. To relate this to mechanics, one horsepower is 745 watts. In order for electricity to do the same work as a one horsepower engine you need 745 electrical watts. This can be one volt at 745 amps, one amp at 745 volts, or even a combination such as 372.5V at 2 amps. To calculate power from voltage and current, current from power and voltage, or voltage from power and current just use the formula;
P = E * I
Say you have a 2.2kW welder and you’d like to know if it can run on a 10A circuit. By using the watt formula you can calculate that that a 2,200W welder running on 120V would need 18.3A, so no, it would not run on a 10A circuit.