Transformers

Transformers have something in common with simple machines: they create a tradeoff between voltage and current.

We have many ways of measuring electricity. Voltage, current, and power are three such quantities.
 * Power (P) is rated in Watts, and provides a measure of how quickly energy is consumed. Lights and other appliances are usually rated in Watts, and the higher the measure, the quicker it gets the job done!
 * Voltage (V) is a measure of the pressure on electrons in the circuit. The higher the voltage, the greater that pressure.  However, the actual flow of electrons encounters resistance, which is not the same in every circuit.  Batteries provide a range of voltages, but are commonly multiples of 1.5 volts.  The US power grid provides household voltage of 110-120 volt.
 * Current (I) is a measure of the flow of electrons in the circuit. The higher the current, the more electrons pass through a point in the circuit every second.  Although current and voltage are related, they are not the same thing (due to the factor of resistance).
 * The three quantities are tied together in an equation: P = V * I.