Pearson Science Double Award Physics 4: Energy Resources and Transfers
Pearson Science Double Award notes on work, power, efficiency, energy stores and generation.
Energy accounting links stores, transfer pathways, heating, work and power. The 4SD0 Double Award boundary ends at point 4.17. Detailed electricity-generation resources at points 4.18 and 4.19 belong to separate Physics and are not assumed here despite the topic's title.
Stores, pathways and conservation
Energy can be held in chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic and nuclear stores. It is transferred mechanically, electrically, by heating or by radiation such as light and sound.
Energy is conserved: it cannot be created or destroyed. A device transfers energy between stores and pathways. Useful output depends on purpose. In a lamp, visible radiation is useful while heating surroundings is often unwanted. Calling energy “lost” is incomplete; it is dissipated to less useful thermal stores.
Efficiency is
The denominator is total input, not useful plus wasted output counted again. Efficiency cannot exceed 100 percent for a correctly bounded passive device.
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