Produce electrostatic charge by friction in a controlled test
Describe an insulated rod-and-cloth procedure and use reference observations to show a charging response without guessing its sign.
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-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.
Before you begin
- Recall electrostatic attraction and repulsion.
- Distinguish a procedure, observation and explanation.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Why compare the same rod at the same detector gap before and after rubbing?
What you will learn
- Describe a simple friction-charging experiment.
- Control moisture, handling and initial detector state when interpreting the result.
Produce and compare a charge response
In a teacher-supervised demonstration, begin with a dry insulating rod and a cloth. Hold the rod by its insulating handle, rub it with the cloth, then bring the rubbed region near an initially neutral electroscope cap without touching it. Compare with the same rod before rubbing at the same distance. Leaf divergence after rubbing is evidence of an electrostatic response.
Keep the detector and supports stable, discharge the detector between comparisons under the teacher's procedure, and avoid touching the rubbed region. Moisture and unintended connections can allow charge to leak away. A poor result can reflect leakage or insensitive apparatus rather than disproving charging by friction.
Interpret the production method
Rubbing brings surfaces into repeated contact and separation, allowing electrons to transfer between the materials. For an isolated initially neutral pair, one loses negative charge and becomes positive while the other gains it and becomes negative. Rubbing does not manufacture charge from mechanical motion.
The sign acquired depends on the material pairing and conditions. Do not assign every plastic rod the same sign without supplied evidence. A detector response alone does not reveal an unknown sign; a known-charge reference and a controlled repulsion comparison can provide that extra information. Paper attraction can demonstrate a response but is also possible through neutral-object polarisation.
Sources for this lesson
Pause and explain
The rubbed rod makes neutral leaves diverge. Which conclusion is justified?
Worked example
A neutral electroscope stays closed near a dry rod before rubbing but diverges when the rubbed rod approaches at the same gap. What is supported?
Show the worked solution
- The rubbing step is the deliberate change.
- The detector shows a new electrostatic response.
- Leaf divergence does not alone identify the rod's charge sign.
Answer The rubbed rod produces an electrostatic response; its sign is not determined by this comparison.
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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 friction-charging test with a rod, cloth and neutral electroscope.
Give me a hint
Separate production by rubbing from detection by approaching the cap.
Compare my reasoning
- Compare the un-rubbed dry insulated rod near the neutral cap.
- Rub it with the cloth while avoiding the charged region.
- Repeat at the same gap and compare the leaf response.
Rub a dry insulated rod and compare its detector response with the un-rubbed control at the same gap.
Look for these in your work
- Include the reference observation.
- Specify non-contact approach and controlled handling.
After rubbing, an initially neutral isolated rod loses electrons to its cloth. Give the two signs and explain their origin.
Give me a hint
Follow the transferred negative charge rather than the mechanical motion.
Compare my reasoning
- The rod loses negative charge and becomes positive.
- The cloth gains negative charge and becomes negative.
- The isolated pair keeps the same total charge.
Rod positive; cloth negative; electrons transferred rather than charge created.
Look for these in your work
- Name both recipients correctly.
- Keep total charge conservation explicit.
A damp rod shows little detector response. Give a plausible limitation and a controlled improvement.
Give me a hint
Check charge retention and the sensitivity reference before rejecting the method.
Compare my reasoning
- Moisture may provide a leakage path.
- Use a dry rod, cloth and insulating support under supervision.
- Check the detector with a known working reference and matched gap.
Leakage or detector sensitivity may hide charging; dry and control the apparatus and check a reference.
Look for these in your work
- Describe a limitation.
- Do not infer zero charge from one weak response.
Common mistakes
- Use a before-rubbing comparison.
- Do not touch the charged region or detector accidentally.
- Detection alone does not identify the sign.
What can you explain now?
Why use a dry insulating support?
Compare with the explanation
To reduce charge leakage.
Moisture or a conducting connection can let the charge leave the region being tested.
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Make it stick
Describe friction production with a controlled detection comparison and explain what its result does and does not establish.
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.