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Measuring Electrical Energy

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 Energy

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  1. Measuring Electrical Energy Lesson 11

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

  3. 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.

  4. 1 watt hour = 3600 joules. • 1 kilowatt hour = 1000 watt hours.

  5. 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.

  6. 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.

  7. Why does circuit two 2 last half of the time that circuit 1 does? • It is using more energy.

  8. 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

  9. 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

  10. 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

  11. 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

  12. Something to remember • Power must be in kW • 1000 W = 1 kW • To change from W to kW divide by 1000

  13. Example • Example 1 • 400 W = ? kW • 400 ÷ 1000 • = 0.4 kW

  14. Example • Example 2 • 15 W = ? kW • 15 ÷ 1000 • = 0.015 kW

  15. Example • Example 3 • 3750 W = ? kW • 3750 ÷ 1000 • = 3.75 kW

  16. Time must be in hours • 60 minutes = 1 hour • To change from min to hours divide by 60

  17. Example 1 • 45 min = ? h • 45 ÷ 60 • = 0.75 hours

  18. Example 2 • 5 min = ? h • 5 ÷ 60 • = 0.08 hours

  19. Example 3 • 90 = ? h • 90 ÷ 60 • = 1.5 hours

  20. 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

  21. 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

  22. Word Problems I (5)

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