ELECTRICAL ENERGY AND POWER - Mr. Shanks' Class



ELECTRICAL ENERGY AND POWER

• ELECTRICAL ENERGY (E) – is defined as the energy transferred to an electrical load by moving charges

- energy is measured in JOULES (J)

• But what is 1 Joule?: 1 Joule of energy can light a 100 Watt

light bulb for 0.01 seconds

• How do you calculate the amount of energy and appliance uses?

E = V x I x t

electrical voltage (V) current (A) time (s)

energy (J)

Example 1 – You use you CD player in the morning. It is plugged into wall outlet

which provides _______ V and the current flowing through the CD

player is 3.2 A. How much energy would your CD player use if you

left it on for 300 s?

Data: Equation:

Substitute:

Calculation:

Answer:

• ELECTRICAL POWER (P) - is a measure of the rate at which energy is being used

- how rapidly an appliance is using up

energy

- power is measured in WATTS (W)

- 1 W = 1 J/s

• If you left a 300 W light bulb and a 100 W light bulb on for one hour, the 300 W light bulb would use 3 times more energy.

300 W ( uses 300 J of energy every second

100 W ( uses 100 J of energy every second

• One Joule represents a very small amount of energy. Since it is so small, energy is also measured in larger units such as the WATT HOUR (W∙h) and the KILOWATT HOUR (kW∙h).

1 W∙h = 3600 J 1 kW∙h = 3 600 000 J

POWER RATINGS FOR COMMON APPLIANCES

|APPLIANCE |AVERAGE POWER |MONTHLY ENERGY |APPROXIMATE |

| |(W) |USE (kW∙h) |COSTS ($) |

|air conditioner |750 |90 – 540 |$7.20 – 43.40 |

|cloths dryer |5000 |50 – 150 |$4.01 – 12.03 |

|coffee maker |900 |4 – 27 |$0.32 – 2.17 |

|computer |600 |5 – 36 |$0.40 – 2.89 |

|electric kettle |1500 |3 – 15 |$0.24 – 1.20 |

|60 W bulb |60 |5 – 30 |$0.40 – 2.41 |

|microwave |1000 |5 – 20 |$0.40 – 1.60 |

|television |80 |5 – 15 |$0.41 – 1.20 |

|toaster |1000 |1 - 5 |$0.08 – 0.41 |

• How do we calculate power?

P = E or P = V x I

t

Power (W) Voltage (V) current (A)

Power in time (s) energy (J)

Watts (W)

Example 2 – Calculate the power of a vacuum cleaner if it operates from the

the wall outlet and the current flowing through it is 7.9 A

Data: Equation:

Substitute:

Calculation:

Answer:

Example 3 – Calculate the power of a toaster that uses 72 000 J of energy in 50 s.

Data: Equation:

Substitute:

Calculation:

Answer:

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