Test electrical conductors and insulators with a complete circuit
Describe an isolated low-voltage sample test with a known conductor and open-gap control, then interpret the indicator carefully.
Section P4.2.1 · Electric charge
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Recognise a complete conducting path.
- Distinguish a sample property from an apparatus fault.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does an open gap do in the simple cell-and-indicator test?
What you will learn
- Describe an experiment to distinguish conduction from insulation.
- Use controls and contacts to interpret a positive or absent response.
Build a comparable sample test
In a teacher-supervised test, use an isolated low-voltage cell, connecting wires and a suitable sensitive indicator in one path. Leave a gap for the test sample. First bridge the gap with a known conducting wire to check the indicator and connections; remove it to make an open-gap control. Insert a dry sample with firm contacts and compare the response.
Use the same supply, indicator and contact positions for the different samples. Ensure current must pass through the sample rather than a bypass wire. An indicator response above the open-gap control supports conduction under the test conditions. Ordinary metals such as copper usually give a clear response; dry plastic or glass usually does not.
Interpret a dark indicator
No visible response may mean an ordinary insulator, but it may also mean poor contacts, an exhausted cell, a faulty indicator or a current below the instrument's detection threshold. Recheck the known conductor and contacts before classifying an unknown. A faint lamp is not a calibrated measure of the sample's conductivity without more information.
Some substances conduct weakly, and moisture or coatings can change the tested path. State the dry sample and apparatus conditions rather than asserting an absolute zero charge motion for every non-response. This written procedure is preparation for practical work, not evidence that the learner has performed it. It uses a supervised low-voltage source rather than household mains.
Sources for this lesson
Pause and explain
Both the sample and known wire give no indicator response. What should happen next?
Worked example
A reference wire lights the indicator, an open gap does not, and a dry copper sample lights it with firm contacts. What is supported?
Show the worked solution
- The reference confirms a functioning circuit and indicator.
- The open gap provides a no-path comparison.
- The copper supplies a conducting path under these conditions.
Answer The copper sample conducts in the tested low-voltage circuit.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Outline a controlled low-voltage conductor/insulator experiment.
Give me a hint
Include one sample path, a conducting reference and an open-gap comparison.
Compare my reasoning
- Connect a cell and suitable indicator with a sample gap in the single path.
- Test a known wire and the open gap to check the apparatus.
- Insert each dry sample with firm contacts and compare responses.
Compare dry sample responses in one low-voltage path against a known conductor and open gap.
Look for these in your work
- Include both controls.
- Check that no bypass avoids the sample.
A wire reference works, copper lights the indicator, and dry plastic does not after contact checks. Classify the samples under these conditions.
Give me a hint
Relate each observation to the functioning reference and instrument limit.
Compare my reasoning
- The wire establishes a working indicator.
- Copper's response supports conduction.
- Dry plastic shows insulating behaviour within the test's sensitivity.
Copper conducts; dry plastic behaves as an insulator within this test's sensitivity.
Look for these in your work
- Use the observed response.
- Keep conditions and sensitivity explicit.
An unknown sample is dark, but a loose clip is found. Does that observation establish insulation?
Give me a hint
Separate contact resistance from the sample material.
Compare my reasoning
- A loose clip can interrupt the path.
- Secure the contact and recheck the conducting reference.
- Repeat the sample comparison before classifying.
No; fix the contact, check the reference and repeat the controlled sample trial.
Look for these in your work
- Identify the confounder.
- Specify the next controlled observation.
Common mistakes
- Keep the sample in the only path.
- Check a reference conductor before interpreting darkness.
- A dark indicator is not proof of exactly zero conduction.
What can you explain now?
Why include a known conducting wire?
Compare with the explanation
To check that the circuit and indicator can respond.
A failed reference warns that a dark sample trial could be an apparatus problem.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Design a controlled conduction test and interpret a non-response without overlooking apparatus or sensitivity.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.