BRAINCAKEEnergy
Revision notes for Energy in OCR Combined Science A (J250). 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 is not a fuel that gets used up.
- Energy store changes in common situationsTo describe a change, say which energy stores go down, which go up, and how the energy is transferred.
- Energy changes: heating, work done by forces and by currentThe energy stored in a system can be changed in three main ways.
- Calculating energy changes on a common scaleWhatever the process, energy is measured in joules (J), so we can add up all the changes on a common scale and show how the energy has been…
- Kinetic, gravitational potential and elastic energyThe kinetic energy of a moving object is given by half × mass × speed squared, or Ek = ½ m v2, with mass in kg, speed in m/s and energy in J.
- Energy dissipationEnergy is never created or destroyed.
- Energy transfers in domestic devicesDomestic devices get their energy from two main sources.
- Power ratings of appliancesEvery domestic appliance has a power rating, shown on a label in watts (W).
- Calculating energy efficiencyEfficiency tells you how much of the energy put into a device is transferred usefully.
- Increasing efficiencyA device is more efficient when a bigger share of its input energy is transferred usefully.
- Lubrication and thermal insulationUnwanted energy transfers can be reduced in two main ways.
- Rate of cooling and wall thicknessA hot object, or a warm house, loses thermal energy to its colder surroundings.