A student was asked to perform an experiment to study the force on a current carrying conductor in a magnetic field. He took a small aluminum rod AB, a strong horse shoe magnet, some connecting wires, a battery and a switch and connected them as shown. He observed that on passing current, the rod gets displaced. On reversing the direction of current, the direction of displacement also gets reversed.
Generated by claude-sonnet-4-6 · 2026-06-15 06:51 · grounding stimulus
Model Answer
(c)
Diagram:
```
↑ (Current flowing upward, out of page at top)
|
← ← | → →
↖ | ↗
← ← • → → • = current coming OUT of page
↙ | ↘
← ← | → →
|
```
The magnetic field lines around a current-carrying straight conductor are concentric circles centred on the conductor.
- The conductor is held vertically; current flows upward (indicated by arrow ↑).
- The magnetic field lines are closed concentric circles in the horizontal plane around the conductor.
- Direction of field lines is determined by the Right-Hand Thumb Rule: wrap the right hand around the conductor with thumb pointing in the direction of current — the curled fingers give the direction of field lines (anticlockwise when current comes towards you).
- Field lines are closer near the conductor (stronger field) and farther apart away from it (weaker field).
Source: Chapter 13 – Magnetic Effects of Electric Current, Oersted's Experiment / Magnetic Field due to Current in Straight Wire
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Explanation
Examiners award marks for: (1) a clear diagram with concentric circles, (2) arrow on the conductor showing current direction, (3) arrows on field lines showing correct direction (anticlockwise for current towards viewer), and (4) mention of Right-Hand Thumb Rule. Make sure the diagram is neat and labelled — roughly 2 marks are for the diagram and 2 for the written explanation/rule.