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P O W E R

P O W E R. Remember when……. Let’s take a brief step back…. But first…. Resistance = charge / current Resistance = volts / amps So … charge = resistance X current current = charge / resistance resistance = charge / current . What is POWER?. Power is defined as

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P O W E R

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  1. P O W E R

  2. Remember when…… • Let’s take a brief step back….

  3. But first… • Resistance = charge / current • Resistance = volts / amps • So … charge = resistance X current • current = charge / resistance • resistance = charge / current

  4. What is POWER? • Power is defined as • Units of Energy / Time • Electrical Power - the amount of electrical power converted to heat, light, sound or motion every second. • Electrical Power - the amount of electrical energy transmitted in a given unit of time.

  5. Symbols of Power • The symbol for power is P • P = energy / time • P = E/T • Energy is measured in joules • P = joules/second • P = watts

  6. The Watt • Named in honour of James Watt (1736-1819) • 1 joule of electrical energy is converted into light and heat by a light bulb every second the power of the bulb is 1 watt. • 60 joules per second is 60 watts

  7. Using the equation… • P = E / t • V (potential difference)= E (energy) / Q (unit of charge) • V = E /Q • E = QxV or just QV • P = E / t becomes P = • We know that is current (or I) …so • P = IV Power = Current x Potential Difference • Remember = power is measured in watts QV t Q t

  8. What you really need to know… • Power (watts) = Current (amps) x Potential (volts) • A current of 13.6 A passes thr ough an electric baseboard heater when it is connected to a 110 V wall outlet. What is the power of the heater? • I = 13.6 • V = 110 V • P = IV = 13.6 x 110 • P = 1496 watts or • P = 1.5 x 103 watts

  9. Power Ratings • Some common household examples in watts: • Hair dryer .................................... 1600 • Deep Fryer ................................. 1500 • Portable Heater .......................... 1500 • Iron ............................................. 1000 • Vacuum Cleaner.......................... 600 • Portable Fan................................. 150 • Television .................................... 150 • Computer ..................................... 150 • VCR............................................... 40 • Stereo ........................................... 30 • Light bulbs.................. 40, 60, 75 or 100 Calculate the current in amps for these appliances P(w) = IV I(a) = P / V V(v) = P / I

  10. Nobody’s Perfect • No device is perfect • Some energy is always converted to heat • Some energy always escapes to the outside • We can calculate efficiency of an appliance • Efficiency % = (energy out / energy in) x100

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