Generated by claude-sonnet-4-6 · 2026-06-15 06:51 · grounding rag
Model Answer
(i) The rule used to find the force on a current-carrying conductor in a magnetic field is Fleming's Left-Hand Rule. Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of current, then the thumb points in the direction of force on the conductor.
(ii)
- (1) Maximum force → Diagram (i) (electron moving vertically upward, perpendicular to the field).
Reason: Force is maximum when the charged particle moves perpendicular to the magnetic field (angle = 90°).
- (2) Minimum (zero) force → Diagram (iii) (electron moving parallel to the field).
Reason: Force is minimum (zero) when the particle moves parallel to the magnetic field (angle = 0°).
Source: Chapter 12, Section 12.3 — Force on a Current-Carrying Conductor in a Magnetic Field
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Explanation
- Examiners award 1 mark for naming Fleming's Left-Hand Rule and briefly stating it.
- For part (ii), identify the correct diagrams AND give the reason based on angle between velocity and field — this is the key concept. Maximum force at 90°, zero force at 0° (parallel). Diagram (ii) is the intermediate case, so it is neither max nor min.
- Note: for an electron, current direction is opposite to its motion, but the angle-based reasoning for magnitude of force remains the same.