Power
Have a look at these two pictures of the Blackpool tower.
What do you think the difference is? One was taken in 1952 and one was taken in 2005?
In 1953 there were 10,000 filament lights this cost approximately £1.368 million a year to power. In 2005 they were switched for 25000 LED lights. It now only costs £410,500 a year. That is a huge saving!
The energy transferred by an electric current depends on the time taken.
Power is the energy transferred per second
This is often shown on appliances as the power rating
Power is measured in watts (W)
1W is a transfer of 1 joule per second.
Power (W) = Energy transferred (J) ÷ Time taken (s)
Time in this equation is needed in seconds
Remember that:
1 minute = 60 seconds
1 hour = 3600 seconds
This equation triangle links power, energy and time.
Remember with equation triangles you cover up the one you are trying to find.
If the letters are next to each other it is a multiplication
If the letters are on top of each other then it is divide
Example
A microwave transfers 48,000J and is used for 60 seconds. What is its power rating?
48,000J ÷ 60s =
800W
Power can also be worked out using:
Electrical power (P) = Current (I) x Potential difference (V)
P= Power measured in watts
I = Current measured in amps
V= Potential difference in volts
Some labels on devices don’t have a wattage on them but give you the current and voltage
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