understanding electricity. electric current electric current: the flow of electrons through a...
TRANSCRIPT
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
• http://www.youtube.com/watch?feature=player_embedded&v=P3kJd3MDeuk
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 per second– Ex: lifting a small apple 1 meter in 1 second
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
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
Energy Calculation Problems
1. How much energy (in Joules) does a 75 Watt light bulb use when it is turned on for 25 minutes?
75 W × (1 J/s / 1 W) × (60 sec/1 min) × (25 min) =
112,500 J
Energy Calculation Problems
2. A 100 Watt light bulb is 20% efficient.a) How many Joules does it use in 12 hours of
operation?
100 W × (1 J/s / 1 W) × (60 sec/1 min) × (60 min/ 1 hr) × 12 hr =
4,320,000 J
Energy Calculation Problems
b) How much energy (in Joules) does the bulb convert to light during 12 hours?
4,320,000 J × 0.2 =
864,000 J light
Energy Calculation Problems
c) How many kWh does it use in 12 hours of operation?
100 W × (1 kW/1,000 W) × 12 hr =
1.2 kWh
Energy Calculation Problems
3. An electric clothes dryer has a power rating of 4000 W. Assume a family does 5 loads of laundry each week for 4 weeks. Each dryer load takes 1 hour to complete.
a) Find the energy used in Joules and kWh.
4000W × (1 J/s / 1 W) × (3600 s/hr) × (1 hr/load) × (5 loads/week) × (4 weeks) = 288,000,000 J
288,000,000W× (1 Wh/3,600s) = 80,000 Wh = 80 kWh
Typical Wattages of Various Appliances
• 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