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S1-3-18 Explain parallel circuits, components, and safety of house wiring. S1-3-21 Develop a formula for power consumption and solve related problems. S1-3-22 Analyze the electrical energy consumption of a household appliance. KEY WORDS OverloadCircuit breakerFuse Power Efficiency

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House circuits are different than the circuits made with batteries: 1.Uses alternating current (AC) instead of direct current (DC) 2.Operates at a higher voltage - 120 V or 240 V 3.Electricity controlled and moved through a main panel (fuse box) 4.All branches off the main line are in parallel Common household circuits are 120 volts and 15 amps

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Remember this? Generators produce A/C current for the home DC: electrons travel in one direction – (-) to (+) AC: e - move back and forth many times a second DC is like rolling balls down a hill – need to keep adding more to the top (or run out) AC is like balls rolling along a teeter totter – don’t need more since they will just move back and forth

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There is also a safety “ground” wire - green or bare copper - removes stray current safely Normal use: 1 hot connected to neutral creates 120 V potential Larger appliances: Both hot wires connect to neutral creates 240 V

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each branch delivers typical 120 volts total current of all branches equals 15 A break any branch without affecting any other All house branch lines link from the main panel. Outlets and switches are all connected in parallel Remember what parallel circuits offer…

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Safety issues: Short circuit: current bypasses the appliance. less resistance – increases branch current Branch heats up – risk of fire There are two components that safeguard against an increase in current Overload: too many things plugged into one outlet. increased branching – increases total current Main heats up – risk of fire A A AA

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main Circuit Breakers: contain either magnet / metal / semiconductor all are altered by excess current - breaks circuit (kill switch) Fuses: uses a strip of metal that easily melts excess current heats metal – breaks circuit Breakers can be reset Fuses “burn out” and need to be replaced A A AA main

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Power and Energy Consumption Power is a measure of energy output over time: running the same distance faster – more power lifting heavier weight in the same time – more power 1 Watt is the power of completing 1 joule of work in 1 second E is energy/work done in joules t is the time in seconds P= t E Power – measured in watts – is the energy used or work done every second

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An iPhone charger moves 72 000 joules of energy in the 4 hours to fully charge a drained battery. What is the power of the charger? P= t E Formula must be in seconds to work properly – time must be converted 4 h · 60 min · 60 sec = 1 h 1 min 14 400 sec P= 14400 seconds 72000 joules = 5 watts (W)

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Rarely do we know energy values, but we can find voltage and current requirements - sometimes they are written on the component. P= t E Remember: Voltage = energy per coulomb of electrons Current = coulombs of electrons per second P= V · I t Q Q E · P=

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A 10 amp car heater is plugged in to a standard house outlet. What is the power of the heater? Large power measurements are converted to kilowatts P= V · I Standard home outlet is 120V P= 120 V · 10 A P= 1200 W 1200 W · 1 kW = 1000 W 1.2 kW

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Energy companies charge a fee for total energy consumption (usually) per month – “hydro” bill Total energy is calculated by multiplying power by time used Purchasing Electrical Energy P is the power in kilowatts (kW) t is the time in hours E= P · t P= t E Notice the units: Time is in hours – seconds are not useful for households Power is in kilowatts – watts are too small to be useful t t

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You make smoothies every day in September (30 days) using a 900 W blender for 15 min. How much energy did the blender use that month? E= P · t 900 W · 1 kW = 1000 W 0.9 kW 15 min · 1 h · 30 (days) = 60 min 7.5 hours E= 0.9 kW · 7.5 h E= 6.75 kWh Energy usage is measured in kilowatt- hours (kWh) instead of joules (too small)

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Reading a Hydro Meter Hydro meter uses 5 dials to measure energy usage: far right dial is “ones” - far left dial is “ten thousands” a reading is taken every 1-2 months Reading 23 930 (kWh) 20 769 (kWh) 3161 (kWh) energy used this month Hydro charges about $0.08 for every kilowatt-hour (kWh) used = $253 this month

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This household uses natural gas for heat and has a second bill for the total amount of gas used. Sample Hydro bill: kWh used Time rate

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Efficiency measures how well a device converts energy into work: every device wastes some energy lost as heat, sound, leakage… If it is more efficient it does the same work with less input energy

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EnerGuide labels give consumers an idea of the efficiency of an appliance: gives energy usage in regular use over time (month/year) allows consumer to estimate cost of using the device efficient devices will have a lower energy usage Energy star: government-regulated symbol used to identify most efficient devices (based on tests). This appliance will use 125 kWh of electricity per month of normal use

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CAN YOU ANSWER THESE QUESTIONS? S1-3-18: How is a household wired to ensure safety? S1-3-21: What is power consumption and how does it affect your electricity bill? S1-3-18: How can you lower electrical energy use of a household? KEY WORDS OverloadCircuit breakerFuse Power Efficiency

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