Original topic practice

Series current: test 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 3.2.2. Parallel circuits, potential difference and resistance remain further study. Specialist review has not been completed.

Foundation · Complete the conducting path

On a paper circuit plan, the cell’s positive terminal connects through a closed switch and a lamp to a loose wire end X. The negative terminal connects to a second loose end Y. Nothing else connects X or Y. All components are suitable and working. Consider these proposed connections on paper only.

Question 1

Which single connection completes a powered series loop through the lamp without bypassing it?

Check the reasoning

Connect X to Y.

Trace positive terminal → closed switch → lamp → X → Y → negative terminal.
A conducting path through the lamp and both cell terminals is required. Do not judge a circuit merely by whether some wires form a closed shape.

Revisit: The complete cell-and-lamp path

Apply · Choose an ammeter connection

A teacher has switched off a suitable low-voltage cell-and-resistor series circuit. A student wants to measure the resistor’s current with one ammeter. The meter’s range, polarity and leads will be checked before the supply is restored.

Question 2

Which plan puts the meter in the required path?

Check the reasoning

Replace a wire section with the ammeter so all resistor current passes through it.

Follow the path through the resistor and then the meter: there should be no extra branch around either.
Use the teacher-supervised low-voltage setup. An ammeter is inserted into the path, not across the cell or the component.

Revisit: Placing and moving the ammeter

Apply · Separate current from energy

Two different filament lamps are working in one unbranched series circuit. After the circuit settles, lamp M appears brighter than lamp N. A student says this proves that more current passes through M.

Question 3

Which response correctly evaluates that claim?

Check the reasoning

Both carry the same steady current; different brightness does not mean current is used up.

Identify the arrangement first: one unbranched path, with steady current.
Separate what is conserved from what can differ. The current is the same; brightness and energy transferred each second need not be.

Revisit: One current through two lamps

Apply · Compare means and ranges

A student takes repeated current readings at positions S and T in the same series circuit. Conditions are controlled as closely as possible. These original constructed data are not laboratory results; no instrument accuracy specification or reference value is supplied.

Illustrative repeated currents (A)
Position	Reading 1	Reading 2	Reading 3
S	0.28	0.30	0.32
T	0.29	0.30	0.31

Question 4

Which comparison is supported by these samples?

Check the reasoning

Both means are 0.30 A; S has range 0.04 A and T has range 0.02 A.

S: (0.28 + 0.30 + 0.32) ÷ 3 = 0.30 A. T: (0.29 + 0.30 + 0.31) ÷ 3 = 0.30 A.
S range: 0.32 − 0.28 = 0.04 A. T range: 0.31 − 0.29 = 0.02 A.
The matching means are consistent with the series-current model. These small samples do not prove exact equality or establish accuracy.

Revisit: Means, spread and the limits of readings

Evaluate · Distinguish position from time

One ammeter is moved between S and T in a single series circuit. The table gives the order of four separate readings. The supply and lamp temperature were not monitored. These original constructed readings are not laboratory results.

Illustrative readings in time order
Order	Position	Current (A)
1	S	0.42
2	T	0.40
3	S	0.38
4	T	0.36

Question 5

Which conclusion and follow-up best fit the evidence?

Check the reasoning

Current may be changing over time; stabilise conditions and repeat with a changed position order.

Compare repeated visits: S drops by 0.04 A and T drops by 0.04 A. The mean at S is 0.40 A; the mean at T is 0.38 A, but the order prevents interpreting that difference as position alone.
Stabilise the supply and temperature, check connections, and repeat with the position order varied. Consider suitable simultaneous measurements if available and checked by the teacher.
Do not infer a specific fault or current consumption from this sequence alone.

Revisit: Controlling conditions and checking drift

Evaluate · Evaluate a consistent meter offset

For this paper model, a checked reference source supplies the exact currents shown. The ammeter always displays 0.03 A above them. Assume that this same additive offset applies between 0.10 A and 0.30 A and that other errors can be ignored. This is an idealised calculation, not a meter-calibration procedure.

Constructed reference comparisons (A)
Reference current	Meter display
0.10	0.13
0.20	0.23
0.30	0.33

Question 6

The meter now displays 0.28 A within this model. What is the corrected current, and would taking repeats alone remove the offset?

Check the reasoning

0.25 A; subtract 0.03 A, and repeats alone do not remove the offset.

Check all comparisons: 0.13 − 0.10 = 0.23 − 0.20 = 0.33 − 0.30 = 0.03 A.
Use reference = display − offset: 0.28 − 0.03 = 0.25 A. This is within the model’s stated reference-current interval.
The model supplies evidence beyond display resolution. In a real measurement, a small range or repeated display alone cannot justify this correction or guarantee accuracy.

Revisit: Resolution, accuracy and measurement limitations

Choose your next step

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.

Return to the series-current lesson · Back to Physics and technology · Explore the series-current mind map