P7.2 Power And Efficiency Flashcards
What is electrostatic store associated with
Separation of charges
What is chemical store associated with
Rearranging atoms
Law of Conservation of Energy
Energy cannot be created or destroyed,
it can only be transferred between stores
If work is done on an object, what is the type of transfer
Mechanical
How do you convert from milliamps to amps
Divide by 1000
Name something that has a thermal energy store
A warm bath
Describe how bread is toasted
Toaster is turned on,
electrical energy is transferred to the thermal store of the heating element
Then thermal energy is transferred by radiation to heat the surface of the bread
What equation links cost of electricity, energy transferred, and cost per unit
Cost of electricity = energy transferred x cost per unit
Define dissipated energy
Energy with no use, lost in the environment
What kind of wall would lose heat the quickest
Thin wall
With high thermal conductivity
Why do high thermal conductivities cool quicker
Energy can be transferred quicker
Efficiency
Measure of how efficiently a device transfers energy from one store to another
Efficiency = useful energy output / total energy input
How can you improve efficiency
Insulating objects, lubricating, energy efficient light bulbs
Sankey diagram
How energy is redistributed when a system is changed
8 energy stores
kinetic, thermal, chemical, elastic potential, gravitational potential, nuclear, electrostatic, magnetic
Example of object with energy in kinetic store
Anything moving
Example of object with energy in thermal store
Anything with temperature
Example of object with energy in chemical store
Anything that can release energy by chemical reaction
Example of object with energy in elastic potential store
Anything stretched like strings and rubber bands
Example of object with energy in gravitational potential store
Anything in gravitational field
Example of object with energy in nuclear store
Atomic nuclei when nuclear reactions happen
Example of object with energy in electrostatic store
2 charges that attract or repel each other
Example of object with energy in magnetic store
2 magnets that attract or repel each other
4 ways energy can be transferred
Mechanically, electrically, by heating, by radiation
How energy is transferred mechanically
Object moving due to force acting on it
How energy is transferred electrically
Charge moving through a potential difference
How energy is transferred by heating
Energy transferred from hotter object to colder object
How energy is transferred by radiation
Energy transferred by light / sound waves
Energy can be stored, transferred between stores and dissipated but…
…energy can never be created or destroyed
