PASCO EM-8656 AC_DC ELECTRONICS LABORATORY - Manual (Page 33)

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012-05892A AC/DC Electronics Laboratory
®
Experiment 11: Ohm's Law II
EQUIPMENT NEEDED:
– Computer and Science Workshop™ Interface
– Power Amplifier (CI-6552A)
– AC/DC Electronics Lab Board (EM-8656): 10
Ω
resistor, 3 V light bulb, and wire leads
– (2) banana plug patch cords (such as SE-9750)
Purpose
The purpose of this experiment is to investigate the relationship between current and voltage in
Ohmic and non-Ohmic materials.
Theory
Ohm discovered that when the voltage across a resistor changes, the current through the resistor
changes. He expressed this as I = V/R (current is directly proportional to voltage and inversely
proportional to resistance). In other words, as the voltage increases, so does the current. The
proportionality constant is the value of the resistance. The current is INVERSELY proportional
to the resistance. As the resistance increases, the current decreases.
If the voltage across an “Ohmic” resistor is increased, the graph of voltage versus current shows
a straight line (if the resistance remains constant). The slope of the line is the value of the
resistance. However, if the resistance CHANGES (that is, if the resistor is “non-Ohmic”), the
graph of voltage versus current will not be a straight line. Instead, it will show a curve with a
changing slope.
For a light bulb, the resistance of the filament will change as it heats up and cools down. At high
AC frequencies, the filament doesn’t have time to cool down, so it remains at a nearly constant
temperature and the resistance stays relatively constant. At low AC frequencies (e.g., less than
one Hertz), the filament has time to change temperature. As a consequence, the resistance of the
filament changes dramatically and the resulting change in current through the filament is inter-
esting to watch.
In the first part of this activity, you will investigate a ten ohm (
Ω
) resistor. In the second part,
you will investigate the filament of a small light bulb.
PROCEDURE
Part A – Ten Ohm Resistor
PART I: Computer Setup
➀
Connect the Science Workshop interface to the computer, turn on the interface, and turn on the
computer.
➁
Plug the Power Amplifier into Analog Channel A. Plug the power cord into the back of the
Power Amplifier and connect the power cord to an appropriate electrical receptacle