BRAINCAKEEnergy
Revision notes for Energy in OCR Physics A (J249). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.
- Conservation of energy in a closed systemEnergy cannot be created or destroyed.
- Changes in energy stores in common situationsWhen a system changes, energy is moved from one store to another.
- Energy changes by heating and by work doneThe energy stored in a system can be changed in three main ways: by heating, by work done by forces, and by work done when a current flows.
- Calculating energy changes on a common scaleTo describe how energy is redistributed in a system, we calculate each change using the right equation, then compare them all in joules (J).
- Kinetic, gravitational potential and elastic energyThree stores can be calculated with equations you need to know.
- Energy dissipationEnergy is never created or destroyed.
- Energy in domestic devicesDomestic devices get their energy in two main ways.
- Power ratings of appliancesEvery domestic electrical appliance has a power rating, shown in watts (W).
- Calculating efficiencyEfficiency tells us how much of the input energy a device transfers usefully.
- Increasing efficiencyTo make a device more efficient we reduce the energy it wastes, so that more of the input energy becomes useful output energy.
- Reducing unwanted energy transferUnwanted energy transfers can be reduced in two main ways.
- Rate of cooling of a buildingA warm building loses energy to the cooler air outside.