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Electricity: Chapter 7

Electricity: Chapter 7. Section 3 B. Protecting the Building. Two ways to control current in wiring Fuse Contains a small wire that melts if too much current heats it Burned out fuse breaks circuit so no more current flows Circuit Breaker Contains piece of metal that bends if overheated

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Electricity: Chapter 7

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  1. Electricity: Chapter 7 Section 3 B

  2. Protecting the Building • Two ways to control current in wiring • Fuse • Contains a small wire that melts if too much current heats it • Burned out fuse breaks circuit so no more current flows • Circuit Breaker • Contains piece of metal that bends if overheated • Switch opens circuit so no more current flows

  3. Electric Power • Power: the rate at which energy is converted from one form to another • Electric power: the rate electricity is converted to another form of energy • Power measured in watts (W)

  4. Electric Power • Power = current x potential difference • Watts = amps x volts • Power often expressed in kilowatts (kW) • P = I V

  5. Electric Energy • Energy used is power multiplied by time • Energy = power x time • Electric energy use measured in kilowatt-hours (kWh) • E = P t • kWh = (kW)(h) • The cost of electricity is the energy times the cost per kWh

  6. Math Skills Activity • You use your fan for 3 hours each day. It has a power rating of 50 W. How much energy does it use in one day? Express your answer in kilowatt-hours. • What we know: • P = 50 W • t = 3 h • What equation: • E = P t

  7. Math Skills Activity Continued • Plug in the numbers! • E = (50 W) (3 h) • Convert W to kW: Use Mr. Boals’ line! • E = (0.050 kW)(3h) • Do the math: • E = 0.15 kWh • Check your answer/units: • Energy units are kWh!

  8. Practice Problem • A 100-W light bulb has a power rating of 100 W. How much energy in kWh is used when you leave it on for 5 h? • Find the power rating for a hair dryer. How much energy is used if you run it for 12 minutes?

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