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Measuring Electrical Energy. Lesson 11. Measuring Electrical Energy. What is Energy? Energy - The ability to do work Electrical Energy - The energy transferred to an electrical load by moving charges.

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measuring electrical energy1
Measuring Electrical Energy

What is Energy?

  • Energy- The ability to do work
  • Electrical Energy- The energy transferred to an electrical load by moving charges.
slide3
The symbol for electrical energy is Eand the SI unit for measuring energy is called the joule.
  • 1 joule is a very small amount of energy so we use Watt hourand Kilowatt hour.
slide4
1 watt hour = 3600 joules.
  • 1 kilowatt hour = 1000 watt hours.
observing sample circuits
Observing sample circuits
  • Circuit 1 has two 1.5 volt batteries in series producing a total of 3.0 volts. The circuit can keep the bulb lit for 5 hours.
slide6
Circuit two has two 1.5 volt batteries in series producing a total of 3.0 volts. There are two bulbs in parallel in this circuit which can stay lit for 2.5 hours.
calculating electrical energy
Calculating Electrical Energy
  • We can use a formula to calculate the amount of energy used in household appliances.
  • Energy = Power x Time
  • kWh kW h
  • Total Energy Used = Speed That Electricity is used x How long electricity is used
how much energy is that
How much energy is that?
  • Examples :
  • How many kilowatt hours of electrical energy are used by a kettle that has a power rating of 1.5kW and is operated for 1.0 hours?
  • Energy = Power x Time
  • E = P x T
  • E = 1.5 kW x 1.0 hour
  • E = 1.5 kWh
slide10
Using a vacuum cleaner runs 2 for hours with a power rating of 1.6 kW.
  • E = P x t
  • E = 1.6 kW x 2 h
  • E = 3.2 kWh
slide11
Mowing a lawn for 3.5 hours with a mower that has a rating of 1.65 kW.
  • E = P x t
  • E = 1.65 kW x 3.5 h
  • E = 5.78 kWh
something to remember
Something to remember
  • Power must be in kW
  • 1000 W = 1 kW
  • To change from W to kW divide by 1000
example
Example
  • Example 1
  • 400 W = ? kW
  • 400 ÷ 1000
  • = 0.4 kW
example1
Example
  • Example 2
  • 15 W = ? kW
  • 15 ÷ 1000
  • = 0.015 kW
example2
Example
  • Example 3
  • 3750 W = ? kW
  • 3750 ÷ 1000
  • = 3.75 kW
slide16
Time must be in hours
  • 60 minutes = 1 hour
  • To change from min to hours divide by 60
slide17
Example 1
  • 45 min = ? h
  • 45 ÷ 60
  • = 0.75 hours
slide18
Example 2
  • 5 min = ? h
  • 5 ÷ 60
  • = 0.08 hours
slide19
Example 3
  • 90 = ? h
  • 90 ÷ 60
  • = 1.5 hours
more examples
More examples

Using a stereo with a rating of 30 W for 2 hours.

  • E = P x t
  • E = (30W ÷ 1000) x 2 h
  • E = 0.03 kW x 2h
  • E = 0.06 kWh
slide21
Using a blender with a rating of 390 W for 20 minutes.
  • E = P x t
  • E = (390 W ÷ 1000) x (20 min ÷ 60)
  • E = 0.39 kW x 0.33 h
  • E = 0.13 kWh
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