LAB # 31 Ohm’s Law
The fundamental relationship among the three important electrical quantities
current
,
voltage
,
and
resistance
was discovered by Georg Simon Ohm. The relationship and the unit of electrical
resistance were both named for him to commemorate this contribution to physics. One statement
of Ohm’s law is that the current through a resistor is proportional to the voltage across the
resistor. You will test the correctness of this law in several different circuits using a Current &
Voltage Probe System and a computer.
These electrical quantities can be difficult to understand, because they cannot be observed
directly. To clarify these terms, some people make the comparison between electrical circuits
and water flowing in pipes. Here is a chart of the three electrical units we will study in this
experiment.
Electrical Quantity
Description
Units
Water Analogy
Voltage or Potential
Difference
A measure of the Energy
difference per unit charge
between two points in a
circuit.
Volts (V)
Water Pressure
Current
A measure of the flow of
charge in a circuit.
Amperes (A)
Amount of water
flowing
Resistance
A measure of how
difficult it is for current to
flow in a circuit.
Ohms (
Ω
)
A measure of how
difficult it is for water
to flow in a pipe.
Figure 1
OBJECTIVES
Determine the mathematical relationship between current, potential difference, and
resistance in a simple circuit.
Compare the potential
vs.
current behavior of a resistor to that of a light bulb.
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APPARATUS
Power Macintosh
wires
Universal Lab Interface
Logger
Pro
Current & Voltage Probe System
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 Fall '08
 RABE
 Physics, Current, Resistance, Resistor, power supply, Electrical resistance

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