SITUATION: You need to add a resistor to a circuit or, even worse, determine what value resistor to use. The calculation of the values of resistors is covered in the lessons.
PARAMETERS: First, keep in mind electronics has many different kinds of resistors and these come in many different packages. But for our projects and lessons we are concerned only with resistors as discrete components. A resistor for us is a small, tubular device that looks like a bit of plastic with a wire coming out of each end. And it has four colored stripes. Of these one is metalic - either gold or silver.
WATTAGE: All our resistors are 1/4 watt unless otherwise specified. This means that if the current going through the resistor is multiplied by the voltage measured across it the result must be 0.25 watts or less. Resistors come in other wattages but with the exception for a few special projects we don't have need for them.
VALUE: The unit of measure of the resistor is the OHM. The value of a particular resistor is encoded in those colored stripes. You can learn to read these strips in How To #4: Read Resistor Values. This instruction may be found in the How-to section of this website.
POLARITY: Many students are confused about which way a resistor needs to be inserted in a circuit to function properly. Happily, a resistor doesn't care. It has no polarity and cannot be connected backward.