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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
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View Full DocumentOBJECTIVES
Determine the mathematical relationship between current, potential difference, and
resistance in a simple circuit. Learn to identify a resistor from its color bands.
Compare the potential
vs.
current
behavior of a resistor to that of a light bulb.
APPARATUS
PC computer
LabPro interface
Wires
Logger
Pro3
Resistor box(200 and 50
Ω
) +/ 1% precision
A Current & Voltage Probe
Light bulb (6.3 V)
DC power supply
Color coded resistor
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 Spring '11
 Hiyishi
 Current, Resistance

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