A resistor, in electrical terms, resists the flow of electrons through it.

Resistance is measured in Ohms. The higher the number, the greater its resistance to current.

Through-hole resistors are color-coded to indicate their resistance value. Here is the table to read resistor values.

Every resistor has a maximum wattage before they burn out. Resistors come in different wattages

Every resistor also has a maximum voltage that it can handle. This is listed on the resistor’s spec sheet.

Surface Mount Resistors
These are common in newer electronics. They became popular in the 1980s and are very common today.

If you are working on vintage circuits, you may run into old-style resistors (dog bone resistors). These were phased out by the early 1950’s.

Why They are Important
Resistors are important to nearly every circuit. They can reduce the voltage and current going to other parts of the circuit.

They can also filter unwanted signals.

Potentiometer (Variable Resistor)
These are very common in many circuits. They are often a way to adjust the volume of an audio circuit or gain for an RF circuit.

The rotary potentiometer is the most common.

PhotoResistor
A photo resistor is an unusual item, but it is common in demonstrations and starter kits. Its resistance changes based on how much light it is exposed to.