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Useful, wasted, and dissipated energy transfers

Useful, wasted, and dissipated energy transfers

Sankey diagram of an electric fan showing electrical energy input splitting into useful kinetic energy of moving air and wasted thermal energy and sound

In a system, energy is transferred between stores when a device works. Total energy is conserved, so energy is not "used up" or destroyed.

7.2 Power and efficiency Lesson

  1. GCSE
  2. /Physics
  3. /7.2 Power and efficiency

Step-by-step lessons on OCR GCSE Physics 7.2 Power and efficiency, covering 7.2.1 Dissipation of energy, 7.2.2 Energy transfers in domestic devices, 7.2.3 Power ratings of domestic appliances, 7.2.4 Efficiency of energy transfers, 7.2.5 Ways to increase efficiency, 7.2.6 Reducing unwanted energy transfers, and 7.2.7 Thermal conductivity and the cooling of buildings. Each one builds up to exam-style questions. Paper 2 and Paper 4 include synoptic questions that draw on Topics P1–P4, so revisit earlier topics before final exams rather than treating each paper as self-contained.

Lessons