A transistor works by allowing a small amount of current applied at the base to control general current flow from collector to emitter through the transistor. A transistor acts as a gate or switch for electronic signals.

Like fuses, circuit breakers stop current flow once it reaches a certain amount. They have the advantage of being reusable (fuses must be replaced when "blown") but respond more slowly to current surges and are more expensive than fuses.

You can multiply the voltage or the current supplied by individual batteries by connecting them together either in series or in parallel. The characteristics of batteries connected in parallel are that total voltage equals the average of the individual battery voltages, total current equals the sum of the individual battery currents, the positive terminal of one battery is connected to the positive terminal of the next, the negative terminal of one battery is connected to the negative terminal of the next, and two connections are made between each adjacent battery.

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 transformer utilizes an inductor to increase or decrease the voltage in a circuit. AC flowing in a coil wrapped around an iron core magnetizes the core causing it to produce a magnetic field. This magnetic field generates a voltage in a nearby coil of wire and, depending on the number of turns in the wire of the primary (source) and secondary coils and their proximity, voltage is induced in the secondary coil.