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Chapter 22Current
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 UnitsWatt (W) = J/s
Ampere (A) = C/sResistance (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
Resistance (R)•Ratio of potential
drop to current flow
Resistance (R)
unit = ohm ()
Resistance (R)
R = V 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
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
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 = I2R
The total electrical energy transferred equals the power
times the time
Energy Formula
E = I2Rt
EnergyEnergy = power x time is measured in kilowatt hours
Formulas
P = VIV = IRP = I2RE = I2Rt
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 in a 12 V system
Calculate: I, P, & E