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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