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Jag Mark
In terms of electrons, how can an
uncharged object become charged?
Electric Power
Notes
Electric Power
All electrical appliances change electrical
energy into another form of energy. For
example, a hair dryer changes electrical
energy into thermal energy.
Electric Power
Power is the rate at which energy is changed
from one form to another. The unit of power is
the watt, which is abbreviated as W. Each
electrical device has a power rating.
Electric Power
The power of an electrical device depends on
the voltage and the current. The equation to
calculate power is:
Power = Voltage X Current
where
Watts(W) = Volts(V) X Amperes(A)
Electric Power
You can use the symbols P for power, V for
voltage, and I for current. Using these symbols,
the power equations can be written this way:
P=VI
Electric Power
Utilizing Ohm’s Law and the equation P=VI, the
following equations can be used to calculate
watts as well:
P=V2/R
or
P=I2R
Electric Power
A clock radio uses the standard voltage of
120V. The clock radio has 0.1A of current in it.
What is the power rating of the clock radio?
Electric Power
A hair dryer has a power rating of 1200W and
uses a standard voltage of 120V. What is the
current through the hair dryer?
Paying for Electrical
Energy
Different appliances change electrical energy
into other forms of energy at different rates.
The more you use an appliance, the more
energy it consumes.
Paying for Electrical
Energy
The equation to calculate the amount of energy an
appliance consumes is:
Energy = Power X Time
The unit of electrical energy is the kilowatt-hour,
which is abbreviated as kWh. One kilowatt is equal to
1000 watts.
Therefore:
Kilowatt-hours = Kilowatts X Hours
Paying for Electrical
Energy
Ten 100W light bulbs turned on for one hour
use 1,000 watt-hours (or 1 kilowatt-hour) of
energy.
E = PT
E = 10(100W) X 1 Hour
Paying for Electrical
Energy
The amount of electrical energy used in your
home is measured by a meter. As more lights
and appliances are turned on, you can
observe a dial on the meter turning more
rapidly.
In general, you pay a few cents for every kWh
of electrical energy you consume.
240V Charger
24kWh Battery Pack
Charges in 8 Hours
What is the current?
Nissan Leaf Charging
Current
E = PT
24kWh = P X 8 Hours
P = VI
P = 24kWh / 8 Hours
3,000W = 240V X I
P = 3 kW or 3,000
Watts
I = 3,000W / 240V
I = 12.5 A
Nissan Leaf Charging
Based on the derived information, how much
resistance does the Leaf system apply to the
current?
Nissan Leaf Charging
Resistance
R = V/I
R = 240V / 12.5A
R = 19.2Ω