P7.2 Flashcards
Where is energy transferred from in electrical devices
Energy is transferred from the chemical store of a battery or from the chemical or nuclear store of fuel in a power station.
How is energy transferred in electrical devices
Energy is transferred when charge moves
What does the power rating of electrical devices tell you
It tells you the rate at which they transfer energy between stores.
What does a larger power rating mean
An increased rate of transfer between stores
What is the unit of energy transferred electrically
Kilowatt hours
Formula for energy transferred electrically
Energy transfered = V x I x t
What do electrical devices do
They change electrical transfer to other forms of energy transfer to do a particular job.
How can you increase the energy in the thermal store
By heating which can be done by burning fuel, using an electric current to transfer energy from a fuel.
What does a temperature difference produce
It produces a transfer of energy from a hot object to a cold object.
When energy is transferred to the surroundings what is it called
Dissipation
How an you reduce energy dissipated by friction
Lubrication
How an you reduce energy dissipated by heating
Insulation
How does lubrication reduce energy dissipated
When you lubricate something, the surfaces are no longer in contact and friction is reduced. Important is reduced energy dissipation.
How do insulators reduce energy transfer
Insulators are materials that don’t conduct well, so the rate of energy transfer is reduced.
What does the rate at which energy is transferred through walls depend on
The thickness of the walls, the material they are made from and the temperature difference.
What happens when the heating is switched on
When the heating is switched on both houses transfer energy to the surroundings until they are both the same temperature.
What do houses with thinner walls do
Energy is transferred to the surroundings quicker
What does a larger temperature difference mean
Energy is transferred to the surroundings quicker
Formula for efficiency
efficiency = useful output energy transfer / input energy transfer
Why are no energy transfers 100% efficient
They aren’t 100% efficient as energy is always transferred to the surroundings.
What diagram can you use to show efficiency
A sankey diagram
What does the width of a Sankey diagram mean
It shows the amount of energy that is transferred
How can you increase efficiency
Use insulation to reduce heating to the surroundings
Make devices from materials that reduce unwanted energy transfer
Use technology to produce devices that are better for their job
