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Circuit Electricity
May 30, 2012
Chapter 22
Terms

Current: Flow of charge
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Symbolized by “I”
Units = Coulombs/second = Amperes (A)
Circuit: a closed loop that current flows
through
 Resistance: Opposition to current
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Units = Ohms (Ω)
LED: Light Emitting Diode
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Used to test for presence of current.
More Terms
Volts: the force that pushes current through a
circuit
 Power: the energy delivered to the circuit per
second
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Power = (current)(voltage)
P = (I)(V)
Units = Watts
Examples #1 & #2
A
car battery causes a current of 2.0
amps through a light while 12 V is across
the battery. What is the power used by
the lamp?
P = (2.0)(12)
 P = 24 W
 What is the current through a 75W lightbulb
connected to a 120 V outlet?
 75 = (I)(120)
 I = .625 A

How does a light bulb light?
As the current flows through the filament, it
encounters resistance
 Resistance: a material’s opposition to current
flow
 Ohm’s Law:
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R = (V/I)
 As resistance increases, current decreases
 As voltage increases, current increases
The collisions between the current and
material results in energy loss (heat and light)
Examples #3 & #4

A car headlight has a resistance of 30Ω and is hooked to
a 12V battery. What is the current through the bulb?
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30 = (12/I)
I = (12/30) = .40 A
A lamp draws a current of .50A when connected to a
120-V outlet. What is the resistance of the lamp?
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R = (120/.50)
R = 240 Ω
Homework
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Ch 22
p 527-529
# 22,23,25,27,30,33,42,45