9478 / 2027

Chapter 15

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, energy per charge, electrical power and measurements, sinusoidal quantities, mean resistive power, rms values and single-diode rectification. For 9478 (2027).

Start readingRevision summaryRead whole chapter

Choose a topic

  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.

  5. Describe an alternating supply

    Read signed current and voltage, define period and peak, and use a sinusoid with a stated time origin.

  6. Mean power and rms values

    Deduce mean sinusoidal heating power and compare it with an equivalent steady current.

  7. Half-wave rectification

    Trace a single-diode circuit in each half-cycle and connect it to the load voltage and current.