A student connects an ammeter and a voltmeter to measure the current through a resistor and the potential difference across it. State where each instrument must be connected in the circuit and explain why each must be connected in that position.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The ammeter must be connected in series with the resistor, so that the same current that flows through the resistor also flows through the ammeter and can be measured.
The voltmeter must be connected in parallel with the resistor, so that it measures the potential difference across the resistor – its two terminals are at the same points as the ends of the resistor.
The voltmeter must be connected in parallel with the resistor, so that it measures the potential difference across the resistor – its two terminals are at the same points as the ends of the resistor.
Examiner tips
- Use the exact wording "in series" and "in parallel". Explain that the ammeter measures current, so it must be part of the current path. Explain that the voltmeter measures potential difference, so its terminals must be at the same potential as the resistor ends.
Common mistakes
- Connecting the ammeter in parallel, which would short it out. Failing to mention that the voltmeter must be across the resistor. Using vague terms like "connected to the circuit" without specifying series or parallel.
Mark scheme (4 marks)
- The ammeter must be connected in series with the resistor.
- So that the same current that flows through the resistor also flows through the ammeter / to measure the current passing through the resistor.
- The voltmeter must be connected in parallel with (across) the resistor.
- So that it measures the potential difference (work done per unit charge) across the resistor / so both terminals of the voltmeter are at the same points as either end of the resistor.
Key terms in this question
ammeter · voltmeter · potential difference · current
Related
- All Cambridge International IGCSE Physics (0625) revision notes →
- How to answer a "State and Explain" question →
- Decode the mark scheme abbreviations →
More Electric circuits questions
- A student connects a battery to a resistor and measures the potential difference…
- Two identical lamps are connected in parallel with each other and then connected…
- A battery is connected to two resistors in series. State what is meant by 'elect…
- A filament lamp and a fixed resistor are connected in series with a battery. Des…