P7: Energy

P7.1 Work done

P7.1a describe for situations where there are energy transfers in a system, that there is no net change to the total energy of a closed system (qualitative only)

P7.1b describe all the changes involved in the way energy is stored when a system changes for  common situations

P7.1c describe the changes in energy involved when a system is changed by heating (in terms of temperature change and specific heat capacity), by work done by forces, and by work done when a current flows

P7.1d make calculations of the energy changes associated with changes in a system, recalling or selecting the relevant equations for mechanical, electrical, and thermal processes; thereby express in quantitative form and on a common scale the overall redistribution of energy in the system (M1a, M1c, M3c)

P7.1e calculate the amounts of energy associated with a moving body, a stretched spring and an object raised above ground level

 P7.2 Power and efficiency

PM7.2i recall and apply: efficiency = useful output energy transfer (J) / input energy transfer (J)

P7.2a describe, with examples, the process by which energy is dissipated, so that it is stored in less useful ways

P7.2b describe how, in different domestic devices, energy is transferred from batteries or the a.c. from the mains

P7.2c describe, with examples, the relationship between the power ratings for domestic electrical appliances and how this is linked to the changes in stored energy when they are in use

P7.2d calculate energy efficiency for any energy transfer

P7.2e describe ways to increase efficiency

P7.2f explain ways of reducing unwanted energy transfer

P7.2g describe how the rate of cooling of a building is affected by the thickness and thermal conductivity of its walls (qualitative only)