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Understanding Efficiency

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Presentation Transcript

  1. Understanding Efficiency Human Circuit

  2. How does it work? • Remember how lie detectors work? People are conductors. • Electricity is nothing more than free electrons moving from atom to atom through a material. This flow is called a current. • Since your body is mostly water and there are water and minerals on your skin, your body can be a conductor, but it’s not a great one.

  3. Direct and Alternating Current

  4. Some motors run on direct current: • Electricity runs in one directions. • Mp3 players, computers, cell phones & calculators also use DC. • Plug-in devices that run on DC come with their own power supplies that convert the power company’s 120-V AC to DC.

  5. The Electricity in household circuits is AC • “Alternating Current” flows back and forth, 60 times per second.

  6. Why do power companies generate AC? • With AC they can use transformers. • Transformers change the amount of voltage with hardly any energy loss. • Changing voltage is necessary because the most efficient way to transmit current over long distances is at a high voltage.

  7. But… • When transmission lines carry current at 500 000 V, the voltage must be reduced before it can be used in your home.

  8. Generating Electricity • Remember our good friend Michael Faraday?

  9. Electromagnetic Induction • Faraday demonstrated that electrical current could be generated (by moving a conducting wire through a magnetic field). • This changed the world because it introduced a way to generate a steady supply of large amounts of electricity. • Generators coils of wire that are moved through a magnetic field.

  10. DC Generator is structurally the same as a DC motor:

  11. AC generator is slightly different:

  12. Power: Rate at which a device converts energy.

  13. Tokyo's Toshima Incineration Plant • Burns 300 tons of garbage a day, turning it into electricity, hot water and a kind of recyclable sand.

  14. The unit of power is: • The Watt (W) – Named for James Watt • A watt is equal to one joule per second. • The faster a device converts energy, the greater its power rating.

  15. Power Ratings: • Most small appliances: 1500 W or less • Stove: 7000 W • Calculator: 0.4 mW

  16. Mathematically: • Power is equal to the current multiplied by the voltage. • Power (P); current (I); voltage (V)

  17. Energy: Measured in Joules (watts x seconds) • You can use the power rating of a device to figure out the amount of energy the device uses. • Remember that power is the rate at which a device converts energy. You can find the amount of energy by multiplying this rate by the length of time the device operates.

  18. Kilowatt Hours • People use a lot of joules of energy in their homes/businesses, so kilowatt hours are often used as a unit for energy. • Calculation is the same, except hours are substituted for seconds, and kilowatts (kW) are substituted for watts. • Electricity meters measure the energy used in kilowatt hours.

  19. Remember what Mr. Edwards taught us?

  20. Law of Conservation of Energy • Energy cannot be created or destroyed. • It does not just appear or disappear… it must be transformed from one form to another.

  21. Read: Page 335-342 • Check & Reflect, page 342, #1-7

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