Extech Instruments MT310 Instrukcja Użytkownika Pobierz pdf (Strona 4)

P31220 Lab

Experiment 3: Building the Potentiometer Circuit (5 minutes)

If you did the “Properties of Resistors” lab, you might recall that the longer the wire, the more

resistance it has. You can think of a long wire as several short segments of wire that are

connected in series. Each segment is a resistor. As you hopefully saw from Experiment 2, the

more resistance you have, the greater the voltage across that resistor. A potentiometer is

basically a long wire with a sliding contact. We can adjust the voltage between two points in the

circuit by moving the slider along the wire. Potentiometers are commonly used for volume and

brightness control knobs.

Connect the circuit shown in Fig. 4. Use the power supply, not the battery. Points a and b are the

outside terminals of the potentiometer as shown in Fig. 3b above. Point w is the middle (wiper)

terminal of the potentiometer. If you have connected everything properly, your DMM should

read 0V when the knob is turned all the way counterclockwise, and some maximum voltage

when the knob is turned all the way clockwise. If this is “backwards”, simply switch the wires

connected to terminals a and b.

Fig. 4: Basic Potentiometer Circuit

Observe that you now have a variable voltage between points a and w. We can now use this

circuit as a variable voltage source for the rest of the lab.

25Ω potentiometer

Fig 3a: Potentiometer. Fig. 3b: Internal construction Fig. 3c: Circuit symbol

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Extech Instruments MT310 Instrukcja Użytkownika Strona 4