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

Open Circuit

ClosedCircuit

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 Megawatt = 1 million 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 (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 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 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. 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