Revision Notes

4.6.2 A.C. & D.C.

Alternating vs Direct Current

  • An alternating current (a.c.) is one that continuously changes its direction, going back and forth around a circuit
  • A direct current (d.c.) is one that is steady, constantly going the same way around a circuit, from positive to negative


ac-&-dc, IGCSE & GCSE Physics revision notes

Two graphs showing the variation of current with time for alternating current and direct current


  • Electric cells (batteries) produce direct current (d.c.)
  • Mains electricity is an alternating current


Exam Tip

If asked to explain the difference between alternating and direct current, sketch the graphs shown above: a well-sketched (and labelled) graph can earn you full marks.


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Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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