P7 Energy Flashcards
Where does an electric current transfer energy from?
From chemical store of a battery
From a chemical or nuclear store of the fuel in a power station
What does the power rating of an appliance mean?
Electrical devices have a power rating which tells you the rate at which they transfer energy between stores. A larger power rating means the appliance will transfer more energy per second you use it
What is the equation for electrical work done and power?
Electric work done (kWh) = Power (kW) * time (h)
What do electrical appliances do?
An electric appliance transfers energy electrically from chemical stores. An electric device changes electrical transfer to other forms of energy to do a particular job
How do appliances change the energy in stores?
Appliances transfer energy between stores. All energy begins in the chemical store and transfers to other stores. As current flows the wire heats up which means some energy is always transferred to the thermal store
How is energy transferred to or from a thermal store?
You can increase the energy in a thermal store by heating such as through burning a fuel or using an electrical current.
Temperature differences produce a transfer of energy from a hot object to a cold object
What is energy dissipation?
Energy that is not used always ends up being dissipated to the thermal stores of the surroundings. This means the energy is no longer in a store that is useful
How can you reduce energy dissipation?
You can reduce energy dissipated due to friction by lubrication
You can reduce energy dissipated due to heating by insulation
How does lubrication reduce energy dissipation?
By placing a layer of fluid between two solid surfaces, they are no longer in direct contact and the friction is reduced
How does insulation reduce energy dissipation?
By placing a material that does not conduct very well between hot and cold objects, the rate of energy transfer is reduced
Why does your house cool down?
The walls, floor, windows and roof transfer energy to the thermal store of the surroundings. To maintain a constant temperature, burning fuel is needed to heat up the surroundings
How does the thickness of the wall affect the rate of cooling?
The rate at which energy transfer through your wall depends on the different thicknesses. A rate of temperature drop is greater if the walls are thinner
How does the thermal conductivity of the walls affect the rate of cooling? Factors?
A room with walls of a higher thermal conductivity will cool down faster.
Factors of thermal conductivity:
Area of the wall
Thickness of the wall
Temperature difference across the wall
What is the equation for efficiency?
Efficiency = Useful Output Energy // Input Energy
What is energy?
Energy is a quantity that tells you what is possible but not what will happen. Energy is simply a scalar magnitude of plausible effect
