OK, let's start by looking at resistors and horse shoes

Apparently the easiest variable in any circuit to control is resistance, so probably the best place to start is with the humble resistor.

As the name would suggest, a resistor, erm, well . . . resists! Yes, it resists current and the lost current is dissipated as heat. Easy so far, right?

The most common schematic symbol for a resistor in a circuit diagram is a zig-zagged line. The resistors are labelled R1, R2, R3 etc, - resistor 1, resistor 2, resistor 3, blah blah and so on and so forth. They are also labelled with their resistance values, expressed in horse shoes. I mean Ohms. (Little joke! Ohm symbol is like an upside-down horse shoe). Anyway, moving swiftly on . . .

There are variable resistors also, just to make things complicated.

And because resistors dissipate heat they are rated according to how much energy they can dissipate without overheating and getting damaged. This is specified by the unit "watts". The power rating of a resistor is generally proportionate to its size, so the bigger the resistor, the higher its power dissipation rating. For more here is a great website - All About Circuits.

Update: Just did a 30-question test on receivers to refresh the memory. Got 29 out of 30 right, 97%. Buachaill Maith!