Transcript Understanding Electricity

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=pl
ayer_embedded&v=P3kJd3MDeuk
Vine Day
Saturday, February 20
9 am – 12 pm
George Lorimer Preserve
North Valley Road Parking Lot
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 per 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
Power Plants
• Limerick’s two reactors produce 2,345
megawatts of electricity in total
• Enough 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 (Wh)
Electrical Consumption
• Electricity is typically sold by
the kilowatt hour (kWh)
• 1 kWh = 1,000 W of power
used for 1 hour
• 1 MWh = 1,000,000 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
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 = 725W
Toaster = 800–1400W
DVD = 20–25W
Vacuum cleaner = 1000–1440W
Water heater = 4500–5500W
Laptop = 50W
Electricity Bill
Energy Calculation Problems
Energy Calculation Problems
• A major coal fired electrical power plant
produces 44,200,000,000 BTU of electrical
energy per day. Assuming that one pound
of coal can produce 5,000 BTU, how many
pounds of coal are used by the plant each
day?
44,200,000,000 BTU x (1lb. coal/5,000 BTU) = 8,840,000 lbs. coal
Energy Calculation Problems
In 2008, the average American home used about 11,000 kWh
of electricity. Suppose the electricity in your region was
supplied by the burning of natural gas. How many cubic feet
of natural gas is needed to support your energy lifestyle?
1 kWh = 3,410 BTU
1 ft3 natural gas = 1,030 BTU
1 BTU = 1,055 J
11,000 kWh x (3,410 BTU/1 kWh) = 37,510,000 BTU
37,510,000 BTU x (1 ft3/1,030 BTU) = 36,417 ft3 natural gas
Energy Calculation Problems
In 2008, the average American home used about 11,000 kWh
of electricity. Suppose the electricity in your region was
supplied by the burning of coal. How many pounds of coal
are needed to be burned?
1 kWh = 3,410 BTU
1 lb. of coal = 12,000 BTU
1 BTU = 1,055 J
11,000 kWh x (3,400 BTU/1 kWh) = 37,510,000 BTU
37,510,000 BTU x (1 lb./12,000 BTU) = 3,125 lbs. of coal
Energy Calculation Problems
A dishwasher has a power rating of 2,000 W. It’s
used for 3 hours each week. If electricity costs
$0.10 per kWh, how much will it cost for a year’s
worth of dishwashing?
2,000 W x 1 kW/1,000W = 2 kW
2 kW x 3 h/week = 6 kWh/week
6 kWh/week x 52 weeks = 312 kWh
312 kWh x $0.10/kWh = $31.20
Energy Calculation Problems
A power plant uses 4,500 tons of coal each day.
Each pound of coal can produce 5,000 BTU of
electrical energy and 3,400 BTU are equivalent to
1.0 kWh of energy. How many kWh of energy are
produced by the plant each day?
4,500 tons/day × 2,000 lbs./ton × 5,000 BTU/lb. ×
1.0 kWh/3,400 BTU = 13,235,294 kWh
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