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ELECTRICAL SYSTEMS 21.3PowerPoint Presentation

ELECTRICAL SYSTEMS 21.3

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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.
- Discuss applications of electricity in daily living.

How much energy is carried by electricity?

Investigation 21BElectrical Energy and 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 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

- Power is a “rate” and is measured using current and voltage.

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

- 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 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

- 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 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 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 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

- 3000 W x 1 kW = 3 kW

= $ 0.90

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 DC

- The electrical system in your house uses alternating current or AC.
- Alternating current constantly switches direction.

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 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

- 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 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.

- 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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