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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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chapter twenty one electrical systems
Chapter Twenty One: Electrical Systems
  • 21.1 Series Circuits
  • 21.2 Parallel Circuits
  • 21.3 Electrical Power
chapter 21 3 learning goals
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.
investigation 21b
Key Question:

How much energy is carried by electricity?

Investigation 21B

Electrical Energy and Power

21 3 electrical power
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.
21 3 electrical power1
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.
21 3 power
21.3 Power
  • Power is a “rate” and is measured using current and voltage.
21 3 kilowatt
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.
solving problems
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.
solving problems1
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
21 3 buying electricity
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.
21 3 buying electricity1
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.
solving problems2
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
solving problems3
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

21 3 ac and dc
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.
21 3 ac and dc1
21.3 AC and DC
  • The electrical system in your house uses alternating current or AC.
  • Alternating current constantly switches direction.
21 3 electricity in homes
21.3 Electricity in homes
  • Electricity comes into most homes or buildings through a control panel which protect against wires overheating and causing fires.
21 3 electricity in homes1
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 3 distributing electricity
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.
21 3 distributing electricity1
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.
slide24

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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