Potential difference: apply the explanation
Try six fresh questions without your notes. Write a reason or calculation before choosing an answer. Use the feedback to find the explanation you need to revisit.
How to use this practice
You can keep your own tally of correct first selections, with six self-check points available. No total or answers are saved by this page. Retries are for learning; these are not official marks or a grade prediction. Written working and partial method credit are not automatically assessed. Completing this practice does not mark the lesson mastered.
Reason about the proposed circuits on paper. These questions do not demonstrate supervised practical competence. Actual measurements require teacher-supervised, suitable low-voltage equipment; never build a mains circuit.
Scope and review status
The questions and data are original. Difficulty labels describe task demands, not exam-board ratings. Grade 8 is StudyForA’s suggested placement, not an official grade requirement. This practice covers an introductory part of England KS3 current electricity and AQA KS3 section 3.2.1. Resistance calculations and parallel networks remain further study. Specialist review has not been completed.
Foundation · Choose the measured component
On a paper plan, two resistors form a series path: A → R1 → B → R2 → C. A and C connect to the positive and negative supply terminals. Connecting wires have negligible voltage drops. A teacher has switched off the suitable low-voltage supply before a voltmeter is connected.
Question 1
Which plan measures the potential difference across R2 while leaving the main path intact?
Check the reasoning
Connect the voltmeter across B and C, with its positive lead at B.
- Identify the two ends of the component, not just any two points in the circuit. R2 lies between B and C.
- Keep the main path intact and add the voltmeter in parallel. Check voltage sockets, range and polarity under teacher supervision before restoring the supply.
Apply · Use energy per charge
In an idealised model, a component transfers 18 J when 3.0 C passes through it. Its potential difference stays constant while a further 5.0 C passes.
Question 2
What is its potential difference, and how much energy is transferred by the further 5.0 C?
Check the reasoning
6.0 V and 30 J.
- V = E ÷ Q = 18 ÷ 3.0 = 6.0 V.
- For the further charge, E = V × Q = 6.0 × 5.0 = 30 J. This is additional energy, not the combined energy for both transfers.
- Energy per charge stays constant; the charge is not consumed.
Apply · Use terminal voltage and series current
A supply labelled 9 V has a measured terminal voltage of 8.4 V while operating. Two resistors are in series; R1 has 2.7 V across it and carries 0.22 A. Assume steady conditions, ideal meters and negligible wire voltage drops.
Question 3
Which values should you assign to R2?
Check the reasoning
5.7 V and 0.22 A.
- V across R2 = 8.4 − 2.7 = 5.7 V.
- R2 current = R1 current = 0.22 A. Separate energy per charge from charge passing per second.
Evaluate · Evaluate a small mismatch
These original constructed readings are not laboratory results. A single voltmeter takes the three readings in sequence; its display step is 0.01 V, but its accuracy specification is not supplied.
| Position | Reading |
|---|---|
| Supply terminals | 7.50 |
| Across R1 | 2.15 |
| Across R2 | 5.32 |
Question 4
What is supply − (R1 + R2), and which interpretation is justified?
Check the reasoning
+0.03 V; investigate measurement limits and changing conditions before drawing a physical conclusion.
- Add the component readings: 2.15 + 5.32 = 7.47 V. Subtract in the stated order: 7.50 − 7.47 = +0.03 V.
- Check the meter specification, connections, possible wire drops and supply stability. Repeat controlled rounds; repetition alone does not remove systematic errors.
Evaluate · Separate changes over time from a voltage balance
One voltmeter is moved between points in a two-resistor series circuit. These constructed readings were taken in the order shown, not simultaneously. The supply was not stabilised.
| Order | Connection | Reading (V) |
|---|---|---|
| 1 | Supply terminals | 4.80 |
| 2 | Across R1 | 1.85 |
| 3 | Across R2 | 2.75 |
| 4 | Supply terminals | 4.40 |
Question 5
Which conclusion and next step best fit the data?
Check the reasoning
The supply changed; stabilise and monitor conditions before comparing readings from the same steady state.
- Supply change: 4.80 − 4.40 = 0.40 V. Component sum: 1.85 + 2.75 = 4.60 V.
- The average supply is also 4.60 V, but the readings do not describe one simultaneous state. Do not infer a specific loss or exact agreement.
- Keep conditions stable and monitor supply voltage during comparisons. Consider checked simultaneous meters under supervision rather than assuming sequential readings are simultaneous.
Evaluate · Apply a stated systematic-error model
In this paper model, exact reference voltages produce the displays below. Assume the same additive offset applies throughout 1.0–6.0 V and all other errors can be ignored. The same meter displays 6.02 V across a supply, 2.02 V across R1 and 4.02 V across R2 in an otherwise steady series circuit. This is not a real calibration procedure.
| Reference voltage | Meter display |
|---|---|
| 1.00 | 1.02 |
| 3.00 | 3.02 |
| 6.00 | 6.02 |
Question 6
Which corrected readings and conclusion follow from the model?
Check the reasoning
6.00 V, 2.00 V and 4.00 V; the corrected values balance, and repeats alone do not remove the offset.
- Each display minus its reference is +0.02 V. The corrected voltages are 6.00 V, 2.00 V and 4.00 V, all within the stated interval.
- Raw residual: 6.02 − (2.02 + 4.02) = −0.02 V. Corrected residual: 6.00 − (2.00 + 4.00) = 0.00 V.
- This conclusion depends on the explicit offset model. A real correction needs appropriate calibration evidence; repeated displays or resolution alone cannot establish it.
Choose your next step
Explore the potential-difference mind map
Revisit any explanation you could not justify, then return to the question and explain why the other options fail. The lesson’s recall check remains separate.
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