March 28, 2011


           Resistors come in dozens of size and shapes but they all do the same thing: Limit current (or resist). More abou that later. First, let's see how a typical resistor is made:

"Carbon Composition" is just a vancy way of describing powdered carbon mixed with a glue-like binder. This kind of resistor is easy to make. And its resistance can be changed from one resistor to the next simply by changing the ratio of carbon particles to binder. More carbon gives less resistance.

Do-It-Your-Self Resistor

You can make a resistor by drawing a line with a soft lead pencil on the sheet of paper. Measure the resistance of the line or points along it by touching the probes of a multimeter to the line. Be sure to set the multimeter to its highest resistance scale. The resistance of a single line may be too high to measure. If so, draw over the line a dozen or so times. Here's what I measured:

Resistor Color Code

See those color code bands on the resistor pictorial? In real life they're kind of pretty. But they have a far more important purpose: they indicate the resistance of the resistor they decorate. Here's how:

Variable Resistor

Often it's necessary to change the resistance of a resistor. Variable resistor are called potentiometers. They are used to alter the volume of a radio, change the brightness of a lamp, adjust the calibration of a meter, etc. Trimmers are potentiometer equipped with a plastic thumbwheel or a slot for a srewdriver blade. They are designed for occasional adjustment.

Resistor Symbol

How Resistor are Used?

Series Circuit
Often resistor are connected in series like this. The total resistance is simply sum of the individual resistance.

Parallel Circuit
Resistor can also be connected in parallel like this. The total resistance is the product of the two resistance divided by their sum.

for three or more in parallel, go find your calculator because...

Voltage Division

Vout is determined by ratio of R1 and R2. Here's the formula:

See also:

Resistor and Capacitor Applications

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