A potentiometer, or "pot" for short, is also known as a variable resistor. Variable resistors are used when it is necessary to dynamically change the resistance in order to control the current in a circuit, and may also be used when a voltage divider is needed. For example, they are used to control the volume in a radio or the brightness of a lamp. They come in many forms and have the same symbol as a resistor, save that they have an arrow pointing towards the middle.
Potentiometers also differ from regular resistors in that they have three terminals instead of two. The terminal in the middle is the "wiper." When a potentiometer is used as a voltage divider, all three terminals are wired separately. But when a potentiometer is used strictly as a rheostat, only need two connections are needed.
Either side of the variable resistor may be attached to the circuit board, with the remaining side unattached or grounded, but it is important to always connect the wiper. The wiper must be grounded or affixed to the voltage source. For example, the left terminal of the pot may be attached to the voltage source and the wiper to ground, or the right terminal may be substituted for the left. Changing the connection to a different side alters the direction the knob must be turned in order to achieve maximum resistance. You may leave the unused side of the variable resistor unconnected, wired to an unused portion of the breadboard, or wired to ground.
In the exercise below, we will practice wiring the variable resistor in different ways in a series circuit.
Things You'll Need
Battery with battery holder
Breadboard
Potentiometer
Multimeter
Low Voltage Led
Resistor
Wire
Switch (optional)
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Instructions
Instructions
1
Begin constructing the schematic on the left by first connecting the battery holder (not shown) to the breadboard.
2
Connect end 1 of the potentiometer to the voltage source, and attach the wiper (terminal 2) to ground. Leave terminal 3 disconnected.
3
Place the limiting resistor and LED combination into the circuit. Do this by adding the resistor in series, and by connecting the positive terminal of the LED to the resistor, and its negative terminal to ground.
4
Secure the battery to the battery holder. Turn the knob on the variable resistor and observe how the LED changes its brightness.
5
Now attach terminal 3 to an unused portion of the breadboard. Test the circuit again.
6
Ground terminal 3 by adding a wire or by moving the connection to the appropriate place on the breadboard. Once more, test the circuit.
7
Repeat all of the preceding steps, but this time use the wiper for the voltage source, terminal 3 for ground, and leave terminal 1 disconnected. Alternatively, just switch the end terminals; use 3 for the voltage source and leave the wiper grounded. Observe how you now have to switch the direction of the knob to achieve the maximum voltage.