Measuring Electrical Energy

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# Measuring Electrical Energy - PowerPoint PPT Presentation

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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Presentation Transcript

### 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.
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.
1 watt hour = 3600 joules.
• 1 kilowatt hour = 1000 watt hours.
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.
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.
• It is using more 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?
• 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
• E = P x t
• E = 1.6 kW x 2 h
• E = 3.2 kWh
• E = P x t
• E = 1.65 kW x 3.5 h
• E = 5.78 kWh
Something to remember
• Power must be in kW
• 1000 W = 1 kW
• To change from W to kW divide by 1000
Example
• Example 1
• 400 W = ? kW
• 400 ÷ 1000
• = 0.4 kW
Example
• Example 2
• 15 W = ? kW
• 15 ÷ 1000
• = 0.015 kW
Example
• Example 3
• 3750 W = ? kW
• 3750 ÷ 1000
• = 3.75 kW
Time must be in hours
• 60 minutes = 1 hour
• To change from min to hours divide by 60
Example 1
• 45 min = ? h
• 45 ÷ 60
• = 0.75 hours
Example 2
• 5 min = ? h
• 5 ÷ 60
• = 0.08 hours
Example 3
• 90 = ? h
• 90 ÷ 60
• = 1.5 hours
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
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