How do you measure voltage, current and resistance, and use instruments to test a circuit safely?
Measuring and testing circuits: connecting voltmeters, ammeters and multimeters, the difference between measuring across and through, and reading circuit and timing signals on an oscilloscope.
An Eduqas GCSE Electronics answer on measuring and testing circuits: connecting a voltmeter in parallel and an ammeter in series, using a multimeter for resistance and continuity, and reading voltage and timing from an oscilloscope.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
Eduqas wants you to measure voltage, current and resistance correctly and to test a circuit with the right instrument: a voltmeter in parallel, an ammeter in series, a multimeter for resistance and continuity, and an oscilloscope for reading the size and timing of changing signals. Sound measurement technique is rewarded directly in the non-exam assessment and in test-based exam questions.
The answer
Measuring voltage with a voltmeter
Measuring current with an ammeter
The multimeter
The oscilloscope
Examples in context
Correct measurement runs through the whole course. You check a potential divider's output voltage with a voltmeter, the current through an LED with an ammeter, a resistor's value with the ohmmeter, and a broken connection with continuity. You read the frequency and mark-space ratio of a 555 astable on an oscilloscope, and you test each subsystem of your non-exam assessment project the same way before joining them together. Examiners often set test-and-measure questions in a practical context.
Try this
Q1. How is a voltmeter connected, and why is its resistance very high? [2 marks]
- Cue. In parallel (across the component); high resistance so it draws almost no current and does not disturb the circuit.
Q2. State the function on a multimeter used to check whether a wire is unbroken. [1 mark]
- Cue. The continuity test (it buzzes for a near-zero-resistance connection).
Q3. One cycle on an oscilloscope spans divisions at per division. Find the frequency. [2 marks]
- Cue. ; .
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas 20203 marksA student wants to measure the current through a lamp and the voltage across it at the same time. Describe how the ammeter and the voltmeter should be connected, and explain why each is connected that way.Show worked answer →
Ammeter (up to 2 marks): connect the ammeter in series with the lamp, in the same current path, so that all the current flowing through the lamp also flows through the ammeter. An ammeter has very low resistance so it does not change the current it is measuring.
Voltmeter (1 mark): connect the voltmeter in parallel with (across) the lamp, so it reads the potential difference between the two ends of the lamp. A voltmeter has very high resistance so it draws almost no current and does not disturb the circuit.
Markers reward "ammeter in series" and "voltmeter in parallel/across" with a correct reason for at least one (low resistance in series, high resistance across).
Eduqas 20213 marksAn oscilloscope is set to per division on the time base, and one complete cycle of a square wave occupies divisions. Calculate the period and the frequency of the signal.Show worked answer →
Period: read the number of divisions for one cycle and multiply by the time base setting. .
Frequency is the reciprocal of the period: .
Markers reward the period and the frequency (using ). A common error is forgetting to convert the period to seconds before taking the reciprocal.
Related dot points
- Circuit concepts: charge, current, voltage (potential difference) and resistance, their units, and Ohm's law relating voltage, current and resistance.
An Eduqas GCSE Electronics answer on the core circuit concepts: charge and current, voltage as energy per coulomb, resistance, their units, and applying Ohm's law to find voltage, current or resistance in a circuit.
- Series and parallel circuits: the rules for current and voltage in each, and combining resistors in series and in parallel.
An Eduqas GCSE Electronics answer on series and parallel circuits: how current and voltage divide in each, the rules that current is shared in parallel and voltage is shared in series, and combining resistors in series (add) and parallel (reciprocals).
- The 555 astable: producing a continuous square-wave output, the frequency and period equations, the duty cycle, and using an astable as a clock or flasher.
An Eduqas GCSE Electronics answer on the 555 timer in astable mode: how it free-runs to give a continuous square wave, the frequency and period equations, why the standard duty cycle exceeds 50 per cent, and using an astable as a clock, flasher or tone generator.
- Interfacing and system design: matching analogue and digital subsystems, signal conditioning between stages, and designing and testing a complete input-process-output system.
An Eduqas GCSE Electronics answer on interfacing and system design: matching analogue and digital subsystems, conditioning a signal between stages so it suits the next block, driving real output transducers, and designing and testing a complete input-process-output system.
Sources & how we know this
- WJEC Eduqas GCSE (9-1) Electronics specification (C490) — WJEC Eduqas (2017)