Measuring electrical energy
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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 energy

Measuring Electrical Energy

Lesson 11


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.


Measuring electrical energy

  • 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.


Measuring electrical energy

  • 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.


Measuring electrical energy

  • 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.


Measuring electrical energy

Why does circuit two 2 last half of the time that circuit 1 does?

  • It is using more energy.


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


Measuring electrical energy

  • 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


Measuring electrical energy

  • 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


Measuring electrical energy

  • Time must be in hours

  • 60 minutes = 1 hour

  • To change from min to hours divide by 60


Measuring electrical energy

  • Example 1

  • 45 min = ? h

  • 45 ÷ 60

  • = 0.75 hours


Measuring electrical energy

  • Example 2

  • 5 min = ? h

  • 5 ÷ 60

  • = 0.08 hours


Measuring electrical energy

  • 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


Measuring electrical energy

  • 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


Word problems i 5

Word Problems I (5)


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