A technician tests two resistors, P and Q, by connecting each one separately to the same power supply. Resistor P allows a large current through it, while resistor Q allows only a small current through it. Explain what these results tell us about the resistance of P and Q, and describe, in terms of electrons and ions, why resistor Q opposes the flow of current more strongly than resistor P.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Resistor P and resistor Q are made from different conducting materials. When connected to the same voltage, P carries a larger current than Q.
Model answer (5 marks)
Resistor P has a lower resistance than resistor Q.
A larger current means more electrons flow per second; a higher resistance opposes the flow of charge.
In resistor Q the positive ions are more densely packed or have a stronger interaction with the moving electrons, so the electrons collide more often.
These collisions transfer energy from the electrons to the lattice, slowing the electrons down and reducing the current.
In resistor P the electrons encounter fewer obstructions and move more freely, so the current is greater.
A larger current means more electrons flow per second; a higher resistance opposes the flow of charge.
In resistor Q the positive ions are more densely packed or have a stronger interaction with the moving electrons, so the electrons collide more often.
These collisions transfer energy from the electrons to the lattice, slowing the electrons down and reducing the current.
In resistor P the electrons encounter fewer obstructions and move more freely, so the current is greater.
Examiner tips
- Use the word "resistance" to link current and voltage; mention electrons and ions explicitly; keep each point short and to the point; use UK spelling.
- Show the cause–effect chain: higher resistance → more collisions → slower electrons → lower current.
- Remember to state that P has lower resistance first, then explain the electron–ion interaction.
Common mistakes
- Confusing resistance with voltage or current; writing that Q has a lower resistance.
- Using vague terms like "more material" instead of electron–ion collisions.
- Forgetting to mention that collisions transfer energy to the lattice.
Mark scheme (5 marks)
- Resistor P has a lower resistance than resistor Q
- A larger current means more charge (electrons) flowing per second / resistance opposes the flow of charge
- In resistor Q, (positive) ions obstruct / collide with the moving electrons more (than in P)
- These collisions transfer energy from the electrons / slow the electrons down, reducing the current
- In resistor P, electrons move more freely / there are fewer obstructions, so current is greater
Key terms in this question
resistance · current · electrons · ions
Related
- All Eduqas A-Level Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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