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Chapter 22
Current
Electricity
Electric Current
•The flow of
charged
particles
Circuit
•Closed loop
through which
charged particles
flow
Voltaic Cell
•Converts
chemical energy
into electrical
energy
Battery
•Several cells
connected
together
Photovoltaic Cell
•Changes light
energy to
electrical energy
Charge Pump
•Increases
potential energy
of the charges
Charge Pumps
•Batteries,
generators,
voltaic cells
Electricity Units
Watt (W) = J/s
Ampere (A) = C/s
Resistance (R) = V/C
Voltage (V) = J/C
Current (I)
•Electric flow
in coulombs
per second
Conventional
Current
The flow of
positive charges
Electric Power
•Product of
potential
difference &
current
Power (P)
P = VI
Resistance (R)
•Ratio of potential
drop to current
flow
Resistance (R)
unit = ohm (W)
Resistance (R)
V
R =
I
Rearranged
V = IR
Resistor
•A device designed
to have a specific
resistance
Resistor
•Made of thin
wires, graphite,
semiconductors,
etc
Resistors
•Light bulb,
toaster, etc
Current can be
changed by
varying either
voltage or
resistance
Potentiometer
•Variable resistor
•rheostat
Schematic
•Diagram of
electric symbols
for components in
a circuit
Electric
Symbols
On page 454
Conductor
Switch
Fuse
Capacitor
Resistor (fixed)
Potentiometer
Ground
Battery
Lamp
Voltmeter
V
Measures Potential
Difference or volts
Voltmeter
V
Must be connected in
parallel with circuit
Ammeter
A
Measures current or amps
Ammeter
A
Must be connected in
series with the circuit
DC Generator
Electric
Connection
No Electric
Connection
When a capacitor is
charged through a
resistor, the current
is high, but falls
quickly
Power dissipated
(used up) in a
resistor is
proportional to the
resistance
Power dissipated in
a resistor is
proportional to the
current squared
Power Formula
P =
2
IR
The total electrical
energy transferred
equals the power
times the time
Energy Formula
E =
2
I Rt
Energy
Energy = power x
time is measured
in kilowatt hours
F
o
r
m
u
l
a
s
P =
V =
P =
E =
VI
IR
2
IR
2
I Rt
A current of 0.50 A
passes through a 120
V outlet for 5.0
minutes: Calculate:
P, R, & E
A 60.0 W light is
connected to a 120 V
outlet for 2.5 hours:
Calculate:
I, R, & E
Headlights burn for
7.5 hrs with a
resistance of 48 W in
a 12 V system
Calculate: I, P, & E