One of the most basic electronic components is the resistor. At first, these components don’t seem very useful; their function is to restrict (or resist) the flow of electrical current through a circuit. With today’s emphasis on efficiency, this seems pointless. However, various effects of resistors’ behavior make them important electronic components — and one of the easiest ones to understand. If you plan on building electronic circuits of more than the absolute minimum complexity, you will eventually need to understand and use resistors. Fortunately, this is easy.

Understanding resistors starts with an understanding of Ohm’s Law. (Voltage is equal to Current times Resistance. Follow the link above for a more in-depth explanation.)

Resistors come in many forms; perhaps the type most commonly used by hobbyists is the 1/4-watt, through-hole fixed-value resistor. These are axial components (meaning they have two connecting wires, initially 180 degrees apart), and are about 2mm in diameter at their thickest part (they would fit inside a typical drinking straw if not bent.) The example resistor shown below is of this type.

Typically, fixed-value through-hole resistors will have four color bands, which specify what the resistor’s nominal value and tolerance (margin of error) is. Here is a chart to help decode what the colors mean:

Here is an example of how these codes would be read on a garden-variety 1-kilohm (or “1k”) resistor. (Click on the image below for a higher-resolution version.) Reading the bands from the left, the brown band represents 1, and the black band represents 0. Putting these together gives “10” for the base value. (The first band is almost never black, except in the unusual case of a “zero-ohm” resistor: a single black band, otherwise known as a “wire.”) The third band is the multiplier band; red signifies multiplication by 100, making the total value 10 x 100 = 1,000 ohms — or “1k.” The 4th band is the tolerance band; gold signifies that the true resistance value of this component should be within 5% of the stated value (950 to 1,050 ohms).

Resistors are used for many tasks in electronics. Without going into too much detail, here is a sampling of some of their many uses: