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.
Core and Extended; Physics 0625, 2026–2028. Use the stated source, operating conditions and meter ranges. Written practice is self-checked.
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.
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.
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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.
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