A student builds a series circuit containing a battery, a switch, and three resistors. Describe what happens to the current in the circuit and the voltage across each resistor when the switch is closed and the circuit is complete.

WJEC GCSE Physics (Wales) — 1.1 Electric circuits · Describe · 4 marks · View as Markdown

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

A battery of fixed voltage is connected in series with a switch and three different resistors. When the switch is open, no current flows.

Model answer (4 marks)

When the switch is closed the circuit is complete and a current flows through the battery, switch and all three resistors.
1. The current is the same at every point in the series circuit.
2. The battery voltage is divided across the three resistors.
3. The resistor with the greatest resistance has the greatest voltage drop across it, while the smallest resistor has the smallest voltage drop.
4. The sum of the individual voltage drops equals the total battery voltage.

Examiner tips

  • Use the word ‘current’ and ‘voltage drop’ to show understanding of series circuits.
  • Show that the current is identical at all points – this is a key point for full marks.
  • Explain that the voltage drop is proportional to resistance – larger R gives larger V drop.
  • Mention that the three voltage drops add to give the battery voltage – this confirms the division of voltage.

Common mistakes

  • Confusing the current in a series circuit with the current in a parallel circuit.
  • Failing to state that the current is the same at every point.
  • Not recognising that the voltage drop is proportional to resistance.

Mark scheme (4 marks)

  1. The current is the same at every point in the series circuit
  2. The total voltage of the battery is shared (divided/split) across the three resistors
  3. A larger resistor has a greater voltage across it (compared to a smaller resistor)
  4. Adding the three individual voltages across the resistors gives the total (battery) voltage

Key terms in this question

series circuit · current · voltage · resistor

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