A-LevelPhysicsElectric fieldsOct/Nov 2010Paper 1 Q291 Mark
A very small oil drop of mass m carries a charge +q. [Figure showing a charged oil drop suspended between two parallel plates. The top plate is negative, bottom plate is positive. Electric field points downwards.] The potential difference across the plates is V and the separation is d. The weight of the drop is balanced by the electric force. (Buoyancy forces may be considered to be negligible.) Which formula gives the charge on the drop?
Aq = mgd / V
Bq = mgV / d
Cq = Vd / mg
Dq = V / (mgd)
✓ Correct Answer
The correct answer is A: q = mgd / V
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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