Understanding Electricity
Electric Current
• Electric current: the flow of electrons
through a conductor (like silver, copper,
gold, or aluminum)
Electrons move in no particular
direction, therefore there is no electric
current
Electrons move in one direction,
therefore there is an electric current
Magnets & Electricity
• An electric current is produced when a
magnet is moved into a coil of wire in a
circuit
Magnets & Electricity
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Open
Circuit
Closed
Circuit
Voltage
• Voltage is the measure of the force that
“pushes” electrons through a circuit
• Similar to the pressure of water pushing it
through pipes
Electric Current
• Current is a flow rate of electrons in a
circuit and is measured in amperes
• 1 ampere (amp) = 6.24 x 1018 electrons
per second
• Similar to the flow of water through pipes
Power
• Power = energy ÷ time
• Ex:
– There is more energy in 1 kg
of coal than 1 kg of TNT
– But, TNT delivers more
power because it releases
its energy in much less time
Electric Power
• Power is the rate that energy is generated
or consumed
• A watt is 1 Joule/second
– Ex: lifting a small apple 1 meter in 1 second
• 1 watt is equal to the rate of current flow
when 1 volt moves 1 amp through a circuit
Putting It All Together
• Watts = Volts x Amps
• Ex: Calculate the wattage of a set of
speakers with 120 V and 2.5 amps.
• W = 120V x 2.5A = 300 W
• Ex: Calculate the amps if the voltage is
120 and the appliance is rated at 650W.
• A = 650W ÷ 120V = 5.4 amps
Scale of Electricity
• Kilowatt = 1,000 watts
– Enough to power an average American home
at any one time
• Megawatt = 1 million watts
– Enough to light a stadium at night
• Gigawatt = 1 billion watts
– Enough to power a major city
• Terawatt = 1 trillion watts
– Annual U.S. consumption is about 0.47
terawatts
Power Plants
• Limerick’s two reactors produce 2,345
megawatts of electricity in total
• Enough energy to power more than 2
million average American homes
Electrical Consumption
• Power is the rate that energy is generated
or consumed, not the amount of energy
• The rate of energy that a light bulb uses at
any moment would be measured in watts
• The amount of energy a light bulb uses
over an entire day would be measured in
watt hours
Electrical Consumption
• Electricity is typically sold by
the kilowatt hour (kWh)
• 1 kWh = 1 kW of power used
for 1 hour
• 1 kWh = 1,000 W of power
used for 1 hour
Relationship Between Energy & Power
• Energy = power x time
• kWh = kW x h
• kWh = energy
• kW = power
• h = time
Relationship Between Energy & Power
• A 10 kW wind turbine can generate 10 kW
of power under optimal conditions
• It would be foolish to ask, “How long does
it take to generate 10 kW?”
– It’s similar to asking, “How long does it take to
travel 10 miles per hour?”
– 10 kW is the rate that it can generate energy,
not the amount of energy it can generate in a
period of time
Relationship Between Energy & Power
• Energy is like distance – it’s an amount
• Power is like speed – it’s a rate
Practice
• Calculate the Watt-hours if you run a
600W hair dryer for 12 minutes. How
many kWh is this?
Typical Wattages of Various Appliances
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Clock radio = 10W
Clothes washer = 350–500W
Clothes dryer = 1800–5000W
Dishwasher = 1200–2400W
Hair dryer = 1200–1875W
Clothes iron = 1000–1800W
Microwave = 750–1100W
Refrigerator (frost-free, 16 cubic feet) = 725W
Toaster = 800–1400W
DVD = 20–25W
Vacuum cleaner = 1000–1440W
Water heater (40 gallon) = 4500–5500W
Laptop = 50W
Electricity Bill