A student has a circuit containing a battery and a single resistor. The student replaces the single resistor with two identical resistors connected in parallel. Explain what happens to the total resistance of the circuit and to the current supplied by the battery after this change is made.

Eduqas GCSE Physics — 1.1 Electric circuits · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

The total resistance of the circuit decreases because the two identical resistors are now in parallel, providing two paths for current to flow.
The current supplied by the battery increases, because the lower resistance allows more current to flow for the same battery voltage.

Examiner tips

  • Use the word ‘decreases’ for resistance and ‘increases’ for current. Explain the reason in one sentence – more paths → lower resistance, lower resistance → more current. Keep the answer concise and use the exact terminology from the mark scheme.

Common mistakes

  • Writing that the resistance increases or that the current decreases. Failing to mention that the resistors are identical. Giving a long, unfocused explanation that repeats the question.

Mark scheme (4 marks)

  1. The total resistance of the circuit decreases
  2. Because there are now more paths for current to flow through
  3. The current supplied by the battery increases
  4. Because the lower resistance allows more current to flow (for the same battery voltage)

Key terms in this question

parallel · resistance · current · battery

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