1. Power generating stations produce large amounts of energy 2. Transformers “step up” the voltage for efficient transmission over long distances 3. Once at the spot, other transformers “step down” the voltage to about 240V/120V used in homes and factories.
4. Distribution lines connect your home to the power grid through a step-down transformer and a power meter. Meter is mounted on outside wall of buildings Records total electric energy supplied to electric devices in the home 5. Electricity now goes to service panel Circuit breaker: at the top of panel, where the wires from the power meter are connected.
6. Main breaker acts as a switch that can cut off all power if the current exceeds the safe level. Bimetallic strip in the breaker heats up, bends, and opens the circuit Older homes have fuse box Metallic conductor that melts when excessive current heats up. 7. Lower part of service panel contains additional circuit breakers for each branch circuit in your home Each branch circuit supplies power to 1 or more wall plugs or lights
Current flow increases when more loads are plugged in. The small resistance of the cable wires causes them to heat up Before it gets TOO hot, the branch breaker cuts off current to all loads in that circuit. Pg. 320, Figure 4.45 Would other devices turn off if this happened in a parallel circuit? NO, other parallel circuit pathways stay on!
What is the difference between: Neutral wire Ground wire Hot wire
Electrical code: a set of standards for electrical work that all electricians must follow
Digital electronic devices are based on: Transistors: Electronic switches turned on and off by electric signals Integrated circuits: Some have several transistors in the same case Microprocessors: chips
Power (P): Energy per unit time Measured in watts (W) Electric power describes the amount of electric energy that is converted into other forms of energy every second.
POWER (in watts (W)) = Energy (in joules (J)) Time (in seconds (s)) P= E t 1 J/s = 1 W
A 100W light bulb converts 100 J of electric energy into light and heat EVERY second. 1 kilowatt = 1000 watts (like kilometres!!) It is more common to measure the voltage and current in a circuit!!
POWER = current X voltage watts amps volts W A V SAMPLE PROBLEM: A current of 13.6A passes through an electric baseboard heater when it is connected to a 110V wall outlet. What is the power of the heater? P= I= V=
Calculating POWER worksheet Remember, for each question, I want to see: - Formula - Work - Answer (in a box!) - /3 marks -
Producing and distributing electricity is expensive! Measured by electric meters. Many power companies measure electric energy in kilowatt hour (kWh) 1 kWh is the total energy supplied to a 1000W load during 1 hour of use TOTAL COST = energy (kWh) X unit cost (cents per kWh)
A family uses 3000kWh of electric energy in a two-month period. If the energy costs 11.0 cents per kilowatt hour, what is the electric bill for the period? Total cost = energy = Unit cost =
To calculate kWh… Energy = Power (W) x Time (h) For example: If a 120W dryer was left on for 3 hours, it would use… 120 W x 3 h = 360Wh = 0.360 kWh 1000 W
A 1500W electric heater in a garage is accidentally left on for 5 full days. If the price of electrical energy is 9 cents per kilowatt hour, how much money was wasted by the running heater unnecessarily?
Remember: 1W= 1 J/s EnerGuide labels are on appliances at home Ex: refrigerators, washers, dryers, air conditioners, etc 1.This large number indicates the approximate amount of energy the appliance will use in one year of use. 2. The coloured bar shows how this appliance compares with others on the market 3.The number gives the yearly energy use of the most efficient and least efficient appliances of similar type 4.Shows the classification of appliance
No device is completely efficient! Some input energy is converted into waste heat! Energy taken in is input energy. Energy that is released is output energy. Efficiency = useful energy output X100% total energy input Read page 328 on how efficient different types of light bulbs are
A 1000W electric kettle takes 4.00min to boil some water. If it takes 1.96 X 10 5 J (196 000J) of energy to heat the water, what is the efficiency of the kettle? Find input value ( E=Pt) Find output value (E=Pt) Then solve with efficiency equation