UNIVERSITY OF MASSACHUSETTS DARTMOUTH
COLLEGE OF ENGINEERING
EGR 101 INTRODUCTION TO ENGINEERING
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This assignment is due Thursday, February 28, 2013.
Use engineering papers.
Show all of your steps.
Present your work neatly and clearly.
Box your final answers.
Configuration A
Configuration B
Consider the 1k potentiometer in either configuration A or B, which are equivalent. In
Configuration A you have the option of leaving one terminal “open” and grounding the
sliding contact. In configuration B you have the option of “shorting” the terminal with
sliding contact. Both configurations accomplish the same objective, i.e., using the
potentiometer as a variable resistor.
In both configurations 0% pot setting indicates the resistance that is “shorted.” For
example if the nominal value of the potentiometer is 1k , then 0% means you have an
effective resistance of 1k in the circuit. If on the other hand you set the “short” to 10%
then the effective resistance in the circuit is 0.9k , and so on and so forth.
1. Generate either configuration in Multisim.
2. Submit a copy of Multisim schematic.
3. Vary the potentiometer setting from 0% to 100% by increments of 5 % and
complete the left three columns in the table below. Generate the table in EXCEL.
4. Complete the right column using Ohm’s law.
5. Show your current calculation using Ohm’s law for a setting of 70%.
I
V
12V
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 40mA
R 300
6. Using the chart wizard in EXCEL plot the current versus resistance for the range
of pot settings from 0% to 100%.
7. Explain how the current changes as a function of resistance, i.e., linearly,
parabolically, hyperbolically, exponentially, etc.
8. What is your observation about the current when the pot setting is 100%?
The current tries to go to infinity when the pot is set at 100% (no effective
resistance).
9. What is the effective pot resistance when the pot setting is 100%?
The effective pot resistance is 0 Ohms.
10. What is the circuit called when the pot setting is 100%?
Short circuit
Pot setting
0%
5%
100%
Pot effective
resistance
k
DMM current
reading
mA
Current based on
Ohm’s law
mA