UNIVERSITY OF MASSACHUSETTS DARTMOUTH
COLLEGE OF ENGINEERING
EGR 101 INTRODUCTION TO ENGINEERING THROUGH APPLIED SCIENCE I
POWER CONTROL USING A POTENTIOMETER - PRELAB
INTRODUCTION
In this experiment, you will use a potentiometer as a variable resistor to control the
brilliance of a light bulb.
The objective of this lab is to have you practice taking voltage and current
measurements, adjusting a potentiometer, using Ohm’s law and power equations and
using known information to infer something about a device.
The circuit you will build is called a dimmer circuit, as shown in Fig. 1.
Figure 1 A lamp dimmer using a potentiometer.
By inserting the potentiometer in series with the lamp (bulb), you can control the current
and hence the power and brilliance of the lamp.
This week, you will put this circuit together on a breadboard and take real
measurements. However, prior to the lab you are charged on your own to simulate this
circuit using MultiSim as explained next.
PROCEDURE: MultiSim Prelab
Use MultiSim to simulate the circuit shown in Fig. 1. To measure current and voltage in
MultiSim, insert an ammeter and 2 voltmeters in the circuit as shown in Fig. 2.
Beginning with the dimmer potentiometer set to 0%, record the current and the voltage
measurements in Excel as shown in Table 1. Repeat the measurements by adjusting
the potentiometer in 25% increments throughout its range. From the voltage and current
measurements determine the resistance of the dimmer potentiometer and the lamp
(bulb). Determine also the power absorbed by the potentiometer and the bulb.
Figure 2 The lamp dimmer with instrumentation.
Table 1 Summary Table for the Dimmer-Lamp Circuit
EGR 101: Name: ___________________________
Dimmer (pot)
Pot setting
(%)
0%
25%
50%
75%
100%
Pot effective
Resistance
( )
Team: _______________
MultiSim Measurements
Current
(A)
Dimmer
Voltage
(V)
Bulb
Voltage
(V)
Calculated
Dimmer
Power
(W)
Bulb
Power
(W)
Bulb
Resistance
( )
DELIVERABLES



Complete the MultiSim simulation individually PRIOR to arriving in lab.
Print a copy of the completed Excel spreadsheet, bring it with you on the day of
the lab and have it initialized by the instructor at the beginning of class in order to
get more than half credit for the lab.
Be sure to attach spreadsheets from every team member to final lab report
(described in second handout).