P7.2 - Power & Efficiency Flashcards
Why do electricity companies use different units as physicists when it comes to electricity bills?
If electricity companies used the same units units and Physicists, people’s electricity bills would be miles of 0’s long. In order to reduce the size of the numbers, electricity companies measure power and time in different units, which ends up changing the units of energy.
What are the units changes used by electricity companies?
Power - Watts, W to Kilowatts, kW
Time - Seconds, s to hours, h
As E = Pt
Energy = kW x h = kWh the kilowatt-hour
What is a kilowatt-hour?
A kilowatt-hour, kWh is a measure of energy not power.
1kWh is the amount of energy transferred by a 1kW appliance, in 1 hour.
Suggest and explain whether using higher-power devices is cheaper, more cheaper, more expensive, or costs the same as using lower-power devices.
Higher power devices transfer electrical energy faster to other forms.
At the same time, they will use more energy so they will cost more to run.
However, if the higher power of the device makes it more efficient at doing its job like a higher power hairdryer drying hair faster,
It won’t need to be on for as long a period of time,
So may actually end up using less energy and so costing less money to use.
What do electrical appliances do?
An electrical appliance transfers energy electrically from chemical stores.
An electrical device changes electrical transfer to other forms of energy transfer to do a particular job.
Analyse the energy transfer for an electric kettle?
Point 1 - When you turn the kettle on
Cold water in the kettle
More fuel/oxygen
More energy in chemical store than the thermal store (- for the water)
TRANSFER A current flow and heats an element in the kettle Energy is transferred electrically Heating by radiation Heating by particles
Point 2 - When the water boils
Boiling water in the kettle
Less fuel/oxygen
More energy in the thermal store (- for the water) and less in the chemical store.
