When used in a circuit, a resistor creates a voltage drop by restricting the amount of power than passes through it. The extra power is dissipated in the form of heat energy. The amount of power dissipated can be calculated using a formula derived from Ohm's law once the voltage in the circuit and resistance of the resistor are known.
Instructions
1. Find the voltage across the resistor. If powered by a battery, you can use the voltage supplied as labeled on the battery. If this is not known, use a voltmeter: set the voltmeter to read voltage and placing the reading ends on either side of the resistor. Write the voltage down.
2. Determine the resistor value by using the color bands and a color code chart or decoding program. A chart can be found by searching "resistor color bands." The first three colors each represent a digit in the resistance value, the fifth is the multiplier in powers of ten, and the final color is the tolerance. Write this result down in Ohms.
3. Calculate the power dissipated by squaring the voltage and dividing it by resistance (P=V^2/R).
Tags: power dissipated, amount power, color bands
