Four basic rules of electronics
Ohm’s law
Probably the most important rule in electronics, ohm’s law states that voltage and current (amperage) are directly proportional:
V = I R
where V is volts, I is amperage, and R (given in Ohms, Ω) is resistance through the circuit.
Ohm’s law is frequently explained in terms of water in a pipe. Volts is the pressure within the pipe, amps is the gallons per second of water flowing through the pipe, and resistance is the size of the pipe (as well as any obstructions). Increase voltage (pressure) and the water flows faster. Add more resistance (say, a partly-open valve), and water flows slower.
What’s this got to do with me?
Take, for example, sound output from a toy. Suppose you wish to replace the speaker with a headphone or line-out jack. A speaker has resistance, usually labelled on the speaker – 8 Ω is common. If you just rip the 8 Ω speaker out and wire in a jack, you’ll be removing the speaker’s resistance, which in turn will increase the amperage (and therefore volume) flowing through the line out (by a factor of 8!). Unless you want to burn out whatever you plug into that jack, you’ll want to put a resistor in series (see below) with the line-out jack. See the article on line-out for more info. (article forthcoming).
So what is an amp?
Strictly speaking, an amp is one coulomb of electrons moving past a point in a circuit in a second. A coulomb, in case you were wondering, is 6,241,509,629,152,650,000 electrons.
You don’t really need to know that. Point is, it’s the flow of electrons.
So what is a volt?
A volt is a measurement of potential difference in a circuit. It’s best thought of as pressure. Current (electrons) flow from high voltage to low voltage, much like water will flow from high-pressure tanks to low-pressure tanks.
It should also be noted that within a DC circuit, current flows from areas of the circuit with larger concentrations of electrons to areas with lower concentrations of electrons. Usually, both the areas are within the same power source, often a battery. The area with the larger concentration (higher voltage) is labelled negative, and the area with lower concentration is labelled positive. If it sounds backwards, that’s because it is – originally, it was thought that electricity was made up of positive charges (protons) instead of negative charges (electrons). But it’s called electronics instead of protonics for a reason.
How about watts?
That one’s easy. Take the volts and multiply by the amps, and you have a unit of actual work, the watt. A 60 watt light bulb, for example, is 60 watts because it is plugged into 120 volt house lines (in the US, in this case) and provides 240 Ohms of resistance, allowing 1/2 an amp through. 120 volts times 1/2 amp is 60 watts.
AC vs DC
You’ve probably heard both of these terms before. AC refers to alternating current, and DC refers to direct current. In an AC circuit, electrons flow in one direction, slow down, and then reverse direction again. This is actually caused by voltage at the power source increasing and decreasing (actually becoming negative) many times per second, which slows down the flow of electrons (see Ohm’s law). The rate at which it does this is measured in hertz – that is, how many times per second. In the US, for example, house current is generally 120volts, 60 hertz. If you’ve ever run a sound cable too near a live power cord, you’ve probably even heard the 60hz tone.