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Circuits and Power

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Series Circuit What happens to the resistance of the circuit as more bulbs are added? –The resistance will increase (light bulbs are resistors) How do you know? –The bulbs are not as bright … ↑ R = ↓ I

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Drawing a Series Circuit

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Series Circuit & Broken Bulbs Why do all the lights turn off when one is unscrewed? –The path is broken – the current needs to go through each light bulb in order to flow (there is only 1 path for the current to take)

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Parallel Circuit What happens to the resistance of the circuit as more “branches” are added? –The resistance decreases – there are several paths for the current to follow ( think about the difference in the flow of water out of a bucket with 1 hole in it verses several holes ) How do you know? –The bulbs are bright … ↓R = ↑I

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Drawing a Parallel Circuit There are different “branches” of the circuit Each bulb is connected to the battery by a separate path

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Parallel Circuits and Broken Bulbs Why does one bulb stay lit when the other is unscrewed? –The current from the battery “splits” up to go through the different branches –The path to the other bulb is not broken – the current can take another path

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Decorative Strings of Lights Which type of circuit would you want your decorative strings of light to have? –Parallel Why? –So the whole string does not go out when one bulb breaks

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Series and Parallel Combo Are all the bulbs the same brightness? Why? Which light bulb can you unscrew to have 1 bulb lit… 2 bulbs lit? A B C

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Series and Parallel Combo Which bulb would be the brightest? Why? B AC Which light bulb can you unscrew to have 1 bulb lit… 2 bulbs lit?

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More Series/Parallel Circuits Which bulb would be the brightest? Why? C B A Which light bulb can you unscrew to have 2 bulbs lit… 0 bulbs lit?

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Ohm’s Law Current – the flow of electrical charge »Unit: Amp »Abbreviation: I Resistance – the measurement of how hard it is for current to flow »Unit: Ohm »Abbreviation: R Voltage – the “force” that causes current to flow »Unit: Volt »Abbreviation: V

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Relationships As Resistance goes up, current goes down As voltage goes up, current goes up

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Formula V = IR Voltage = current x resistance V = IR I = V÷R R = V÷I V IR

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Power Power = The rate at which energy is transformed from one form to another –electrical energy to thermal energy –electrical energy to mechanical energy –electrical energy to light energy

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Power Potential Energy for a circuit? Voltage Rate of flow of energy? Current (remember this means # charges flowing past a point per second) So what does power equal? Power = Voltage x Current P = VI Unit = Watt

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Formula P = VI Power = Voltage x Current P = VI V = P÷I I = P÷V P VI

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Do Just Light Bulbs have a Wattage? Typical Wattages of Various Appliances Here are some examples of the range of nameplate wattages for various household appliances: Aquarium = 50–1210 Watts Clock radio = 10 Coffee maker = 900–1200 Clothes washer = 350–500 Clothes dryer = 1800–5000 Dishwasher = 1200–2400 (using the drying feature greatly increases energy consumption) Dehumidifier = 785 Fans –Ceiling = 65–175 –Window = 55–250 –Furnace = 750 –Whole house = 240–750 Hair dryer = 1200–1875 Heater (portable) = 750–1500 Clothes iron = 1000–1800 Microwave oven = 750–1100 Personal computer –CPU - awake / asleep = 120 / 30 or less –Monitor - awake / asleep = 150 / 30 or less –Laptop = 50 Radio (stereo) = 70–400 Refrigerator (frost-free, 16 cubic feet) = 725 Televisions (color) = 65 – 170 Toaster = 800–1400 Toaster oven = 1225 VCR/DVD = 17–21 / 20–25 Vacuum cleaner = 1000–1440 Water heater (40 gallon) = 4500–5500

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Electric Bills - FYI The cost of electricity is based on: –Power use of the building (kW) –Amount of time power was used (hr) –Power x Time = Energy use (kWh) The power company then multiplies your energy use by a generation rate (and adds various fees as well)

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