A vertical wire carries a current directed straight upward. Using the right-hand thumb rule, determine the direction of the magnetic field at a point (i) to the north of the wire, and (ii) to the east of the wire. Explain your reasoning in each case.
Generated by claude-sonnet-4-6 · 2026-06-26 01:11 · grounding rag
Model Answer
The magnetic field around a vertical current-carrying wire forms concentric circles in the horizontal plane, with direction given by the right-hand thumb rule: point the right thumb upward (direction of current); the fingers curl in the direction of the magnetic field.
(i) To the north of the wire: The fingers at the north side curl from east to west, so the magnetic field points towards the west.
(ii) To the east of the wire: The fingers at the east side curl from north to south, so the magnetic field points towards the south.
Source: Chapter 12, Section 12.2.2 — Right-Hand Thumb Rule
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Explanation
- The key step is applying the right-hand thumb rule correctly: thumb = current direction (up), curling fingers = field direction.
- Visualise the wire from above: the field circles anticlockwise when viewed from above (since current is upward). At the north point, anticlockwise means the field goes west; at the east point, it goes south.
- Examiners award 1 mark for stating the rule, 1 mark for each correct direction with brief reasoning. Don't just state directions — mention the rule and curl direction.