ELECTRICAL SYSTEMS 21.3
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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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ELECTRICAL SYSTEMS 21.3

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Electrical systems 21 3

ELECTRICAL SYSTEMS 21.3


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 important review

21.3 Important review


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 different forms of the power equation

21.3 Different forms of the Power Equation


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.


Electrical systems 21 3

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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