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ELECTRICAL SYSTEMS 21.3

ELECTRICAL SYSTEMS 21.3. Chapter Twenty One: Electrical Systems. 21.1 Series Circuits 21.2 Parallel Circuits 21.3 Electrical Power. Chapter 21.3 Learning Goals. Define electric power and apply a formula to perform power calculations. Distinguish direct current and alternating current.

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ELECTRICAL SYSTEMS 21.3

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  1. ELECTRICAL SYSTEMS 21.3

  2. Chapter Twenty One: Electrical Systems • 21.1 Series Circuits • 21.2 Parallel Circuits • 21.3 Electrical Power

  3. Chapter 21.3 Learning Goals • Define electric power and apply a formula to perform power calculations. • Distinguish direct current and alternating current. • Discuss applications of electricity in daily living.

  4. Key Question: How much energy is carried by electricity? Investigation 21B Electrical Energy and Power

  5. 21.3 Electrical Power • Electrical power is measured in watts, just like mechanical power. • Power is the rate at which energy is changed into other forms of energy such as heat, sound, or light. • Anything that “uses” electricity is actually converting electrical energy into some other type of energy.

  6. 21.3 Important review

  7. 21.3 Electrical Power • The watt is an abbreviation for one joule per second. • A 100-watt light bulb uses 100 joules of energy every second.

  8. 21.3 Power • Power is a “rate” and is measured using current and voltage.

  9. 21.3 Different forms of the Power Equation

  10. 21.3 Kilowatt • Most electrical appliances have a label that lists the power in watts (W) or kilowatts (kW). • The kilowatt is used for large amounts of power.

  11. Solving Problems • A 12-volt battery is connected in series to two identical light bulbs. • The current in the circuit is 3 amps. • Calculate the power output of the battery.

  12. Solving Problems • Looking for: • …power of battery • Given: • …voltage = 12 V; current = 3 amps • Relationships: • Power: P = I x V • Solution: • P = 3 A x 12 V = 36 watts

  13. 21.3 Buying Electricity • Utility companies charge customers for the number of kilowatt-hours (kWh) used each month. • A kilowatt-hour is a unit of energy. • The number of kilowatt-hours used equals the number of kilowatts multiplied by the number of hours the appliance was turned on.

  14. 21.3 Buying Electricity • There are many simple things you can do to use less electricity. • When added up, these simple things can mean many dollars of savings each month.

  15. Solving Problems • How much does it cost to run a 3,000 kW electric stove for 2 hours? • Use an electricity cost of $0.15 per kilowatt-hour. • Looking for: • …cost to run stove for 2h • Given: • … P = 3,000W;T = 2h; price $0.15/kW

  16. Solving Problems • Relationships: • 1000 watts = 1 kW • Charge in kWh • Solution: • 3000 W x 1 kW = 3 kW 1000 W • Charge = 3 kW x 2 h = 6 kWh • Cost = 6 kWh x $ 0.15 1 kWh = $ 0.90

  17. 21.3 AC and DC • Although the letters “DC” stand for “direct current” the abbreviation “DC” is used to describe both voltage and current. • DC current flows in one direction as in a battery.

  18. 21.3 AC and DC • The electrical system in your house uses alternating current or AC. • Alternating current constantly switches direction.

  19. 21.3 Electricity in homes • Electricity comes into most homes or buildings through a control panel which protect against wires overheating and causing fires.

  20. 21.3 Electricity in homes • Electrical outlets in bathrooms, kitchens, or outdoors are now required to have ground fault interrupt (GFI) outlets. • GFI outlets are excellent protection against electric shocks, especially in wet locations.

  21. 21.3 Distributing electricity • Electricity is a valuable form of energy because electrical power can be moved easily over large distances. • Alternating current is easier to generate and transmit over long distances.

  22. 21.3 Distributing electricity • Many electronic devices, like cell phones or laptop computers, use DC electricity. • An “AC adapter” is a device that changes the AC voltage from the wall outlet into DC voltage for the device.

  23. Bright Ideas • What makes one bulb more efficient than another? How much more efficient are the LEDs? What kind of savings does this mean in terms of electricity?

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