Describe a force experiment with a current-carrying conductor
Plan a controlled observation of a movable conductor in a magnetic field with current-on and current-off references.
Cross-referenced from the related Cambridge IGCSE Chemistry 0620 or Physics 0625 teaching to the 0652 syllabus. Exact 0652 Core/Supplement objective coverage and this final-series course’s examiner fit still need specialist review. Written practice is self-checked and does not predict a Cambridge grade or demonstrate supervised laboratory competence.
Before you begin
- Trace a complete current path.
- Distinguish a force from observed motion.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does a closed conducting loop permit?
What you will learn
- Plan a controlled observation of a movable conductor in a magnetic field with current-on and current-off references.
- Describe a controlled movable-rod method and distinguish force evidence from calibrated magnitude.
Allow the conductor to move
A suitable school demonstration places a light movable conducting rod across two conducting supports in the gap between magnetic poles. A supervised low-voltage, current-limited circuit passes conventional current through the rod. The supports permit displacement rather than clamping the rod rigidly. A magnetic force on the current-carrying rod can then produce observable movement.
Observe a current-off reference first, then briefly close the circuit under the stated apparatus limits. Compare movement with current on and off while pole arrangement, support friction and rod placement stay unchanged. A fixed rod may experience a force without visible displacement; absence of movement alone is not proof of no force.
Keep the evidence and method distinct
A supplied observation table can show that movement changes when the electrical or magnetic condition changes. It does not by itself give a calibrated force value: displacement also depends on friction, mass, supports and observation time. Contact heating and a nearby return conductor can confound the arrangement.
Use approved apparatus, suitable ratings and the teacher’s supervision; this is a written description, not an instruction to connect a loose conductor to mains electricity. Reversing current and field are developed as separate comparisons in the next lessons. Written planning does not demonstrate supervised practical competence.
Sources for this lesson
Pause and explain
A clamped rod does not move. Is that enough to establish no magnetic force?
Worked example
A movable rod shifts when the supervised circuit is closed but stays still with current off. What can this demonstrate, and what does it not measure?
Show the worked solution
- The current-on condition supplies a magnetic interaction with the imposed field.
- The controlled displacement is evidence of a force.
- Displacement alone is not a calibrated force measurement.
Answer Evidence of a current-dependent force; no numerical force follows from displacement alone.
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.
Describe apparatus and references for a conductor-force demonstration.
Give me a hint
Name the movable part and the controlled on/off comparison.
Compare my reasoning
- Place a movable rod across suitable conducting supports in a pole gap.
- Use the specified supervised current-limited circuit.
- Compare current off with briefly on under matched conditions.
A controlled movable-rod observation with on/off references.
Look for these in your work
- Name the field and current path.
- Retain supervision and apparatus limits.
Explain why a large displacement is not automatically a large calibrated magnetic force.
Give me a hint
Consider other causes of the observed motion.
Compare my reasoning
- Support friction can vary.
- Mass and observation time affect displacement.
- Force size needs separate calibrated information.
Displacement alone does not determine force magnitude.
Look for these in your work
- Separate force evidence from size.
- Name at least two confounding conditions.
A report changes rod mass, supports and current together, then attributes all movement change to current. Critique it.
Give me a hint
Identify variables that also affect motion.
Compare my reasoning
- Mass and supports change the response.
- Current is not the only changed factor.
- Retain the same rod and supports for a current comparison.
The comparison is confounded; hold mechanical conditions fixed.
Look for these in your work
- Identify changed variables.
- Propose a matched comparison.
Common mistakes
- Permit movement in the apparatus.
- Use an off reference and consistent supports.
- Do not infer force size directly from displacement.
What can you explain now?
Why should the rod be movable in this demonstration?
Compare with the explanation
To make a force’s effect observable
A movable supported rod can show displacement; a clamp can mask that effect.
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Make it stick
Describe a controlled movable-rod method and distinguish force evidence from calibrated magnitude.
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.