8867 / 2027

Chapter 8

Currents

Name the cross-section for current, the endpoints for voltage and the system receiving electrical energy.

Explain how charge motion transfers energy, calculate power under stated conditions and assess measurements of input and useful output.

Current and drift velocity, potential difference and e.m.f., electrical power, and matched electrical-input and mechanical-output measurements. For 8867 (2027).

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  1. Charge flow and drift

    Derive current from a carrier-density model and distinguish net drift from irregular microscopic motion.

  2. Energy per charge

    Use a potential reference and distinguish source e.m.f., terminal p.d. and internal energy transfer.

  3. Electrical power and energy

    Derive the three power expressions, identify what is held fixed and calculate energy over a stated interval.

  4. Measure input and useful output

    Place meters at the chosen load and compare motor-terminal input with useful lifting work over the same events.