Nuts and Volts - May 2010

FUNDAMENTALS FOR THE BEGINNER

WHAT A POTENTIOMETER DOES

This potentiometer is being used as a rheostat or variable resistor. Its function is to vary the resistance in electronic circuits and devices. For example, they are used in radios and TVs to control the volume of the audio in the speaker. A “pot” can also be used as a voltage divider. By doing this experiment, you will see that a potentiometer can vary the resistance in a circuit and, in this case, the brightness of the LED.

Schematic

1. Build the Circuit.

Using the schematic along with the pictorial diagram, place the components on a solderless breadboard as shown. Verify that your wiring is correct.

2. Do the Experiment.

Theory: This electronic circuit consists of an LED, a 100 ohm resistor (to keep the LEDs from burning out from too much current when the potentiometer is adjusted to zero ohms), a nine-volt battery, and a potentiometer. The electrons flow from the battery through the resistor, through the LED, through the potentiometer, and back to the battery. The higher the resistance in the circuit, the fewer the electrons that will flow.

Procedure: Connect a nine-volt battery to the battery snap and observe the brightness of the LED. Now, turn the shaft fully clockwise and then fully counter-clockwise. As you turn the shaft, the resistance varies through the potentiometer and this will cause the LED to get brighter and dimmer.