Explain electron transfer when solids are rubbed
Track electron loss and gain while keeping positive constituents in the solid and separating charging from redistribution.
Core and Extended; Physics 0625, 2026–2028. Follow the selected magnetism or charge section. Field lines are explanatory models, not material threads or measured force values. Written practice is self-checked.
Before you begin
- Determine charge imbalance.
- Describe friction charging and detection.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which constituent carries negative elementary charge?
What you will learn
- Explain friction charging as transfer of negative charge only.
- Determine each object's sign from a supplied electron-transfer direction.
Move negative charge between solids
In the simple solid friction-charging model, the particles transferred are electrons. Positive constituents remain in their solid structures. If electrons move from solid A to solid B, A loses negative charge and becomes more positive while B gains negative charge and becomes more negative.
For two initially neutral isolated model objects with ten positive and ten negative units each, transfer three electrons from A to B. A keeps ten positive units and now has seven negative units, giving +3. B keeps ten positive units and has thirteen negative units, giving −3. The positive counts did not increase or move.
Respect the supplied starting state
Electron loss means a positive change in net charge, but it does not always make an already charged object positive. A starting net charge of −5 units that loses two electrons becomes −3 units, which is still negative. Combine the initial imbalance and the transfer rather than assuming neutrality without permission.
Charging by transfer changes the total charge of an individual object across its boundary. Redistribution moves charge between regions of one object without changing that object's total. Both can affect a detector, so explain the process specified. Material choice and conditions determine the transfer direction; friction alone does not tell you which object receives electrons.
Pause and explain
Electrons transfer from neutral A to neutral B. Which description is correct?
Worked example
A model solid begins with net −5 units and loses two electrons. Find its final net charge.
Show the worked solution
- Each lost electron removes one negative unit.
- The object's net charge changes by +2 units.
- −5 + 2 = −3 units.
Answer −3 elementary charge units; less negative, still negative.
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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.
Two neutral model solids each contain ten positive and ten negative units. Move three electrons from A to B and calculate each net charge.
Give me a hint
Keep the positive counts fixed and change only the electron counts.
Compare my reasoning
- A has ten positive and seven negative units: +3.
- B has ten positive and thirteen negative units: −3.
- The transferred particles are electrons.
A: +3; B: −3 elementary charge units.
Look for these in your work
- Keep the ten positive units in each object.
- Apply the specified transfer direction.
A solid has net +4 units and gains six electrons. Find its final net charge.
Give me a hint
Adding each electron changes net charge by −1 unit.
Compare my reasoning
- Start from +4 units.
- Add a change of −6 units.
- +4 − 6 = −2 units.
−2 elementary charge units; negative.
Look for these in your work
- Include the starting charge.
- Allow the sign to cross zero.
A learner explains a positively charged rubbed rod by protons moving into it. Correct the mechanism.
Give me a hint
Use electron deficit without relocating the positive solid constituents.
Compare my reasoning
- The solid's positive constituents remain in place.
- The rod can become positive by losing electrons.
- The recipient material gains the negative charge in an isolated pair.
The rod loses electrons; positive constituents do not transfer into it in this model.
Look for these in your work
- Identify the moving particles.
- Account for the recipient of the electrons.
Common mistakes
- Electrons move in ordinary solid friction charging.
- Electron loss makes charge more positive, not always positive.
- Use the given starting balance.
What can you explain now?
An initially neutral solid gains electrons. What sign follows?
Compare with the explanation
Negative.
Adding negative charge creates an electron excess over the fixed positive contribution.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Track electron transfer from any stated starting charge while leaving positive solid constituents fixed.
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.