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Electricity in Your Home A power grid is a network that connects electricity generating facilities, transmission lines, distribution stations, transformers, homes, and businesses. In Canada the grid connects almost all regions. As demand fluctuates, power is regularly shifted from province to province. Alberta might draw power from BC during peak periods. Read page 318 Transformers are used to: Step up transformers are used to increase the voltage. The purpose is for efficient transmission of electricity over long distances. Step down transformers are used to decrease the voltage. They are found before the electricity enters homes and businesses. Read page 318-319 Activity on page 321. Hand in your sample floor plan (#3), and a sample room circuit diagram (#2). Hand in #1 and #2 from “What did you find out” Read page 322. The similarity between household circuits and microelectronic circuits is that they perform the same basic function: to power an electrical device. The main difference between household circuits and microelectronic circuits is the scale. FYI – Transistors (on digital devices) act as switches turning current on and off and act as amplifiers increasing the strength of an electric signal as it passes through the transistor. Microprocessing units (MPU) and CPUs are large, complex circuits built on a tiny piece of silicon. At their core are millions of transistors connected by fine traces of aluminum (conductors and pathways). A MPU functions are dictated by software that gives the chip its instructions. Todays most advanced chips contain more than 42 million transistors and are continually becoming smaller and smaller. Measuring Electric Power Power (P) - the rate at which a device converts energy. - energy per unit time. - Measured in watts. There are two equations that describe power relationships: P = IV E = Pt Example: A current of 13.6 A passes through an electric baseboard heater when it is connected to a 110 V wall outlet. What is the power of the heater? I = 13.6 A V = 110 V P = IV = 13.6 X 110 = 1496 W Example: How many joules of energy does a 1200 W hair dryer use in 10 minutes each morning? P = 1200 W T = 10 mins or 600 seconds E = Pt = 1200 X 600sec = 720 000 J Example: A 100 W light bulb is plugged into a 120 V outlet and is on for 5 minutes. a) What is the current? P = 100 W V = 120 V T = 5 minutes = 300 seconds P = IV I=P/V = 100 W / 120 V = 0.83 A b) What is the energy used? E = Pt = 100 X 300sec = 30 000 J Work on questions #1-4 on page 324. BLM 4-18 Read page 324 NOTE: Figure 4.47 a GOOD EXAM QUESTION Given that 1 kW = 1000 W 1 hour = 60 minutes = 3600 seconds kWh (kilowatt hours) = kW (kilowatts) X h (hours) The cost of power ($) = kWh X $/kWh See model problem on page 325. On page 325 #1-3 BLM 4-19 BLM 4-20 Power rating – read page 326. Almost all electrical devices are labeled with their power rating or the number of watts they consume every second they are operating. If consumers know the current rate per kWh that they are paying for electricity, they can calculate the amount of money they would save by buying one brand over another. Electrical Devices and Efficiency Efficiency = useful energy output X 100 Total energy input FYI the efficiency of a car engine is about 25%. Go over the model problem on page 329. On page 329 #1-3 BLM 4-22 Home Electric Safety Read pages 330 – 331 Ways to reduce waste of energy in common household devices: - using more efficient forms of lighting (halogen bulbs) - pick energy efficient appliances - don’t leave lights on - use full loads of laundry and dishes - add insulation around stoves, windows, etc. On page 331 #1-4