A current-carrying straight wire is held vertically and you look at it from the top. The current flows upward (towards you). Using the right-hand thumb rule, determine the direction of the magnetic field lines — are they clockwise or anti-clockwise as seen from the top? Justify your answer.
Generated by claude-sonnet-4-6 · 2026-06-26 01:11 · grounding rag
Model Answer
Direction of magnetic field: Anti-clockwise (as seen from the top).
Justification using Right-Hand Thumb Rule:
Hold the vertical wire in the right hand such that the thumb points upward (direction of current, i.e., towards you). The fingers curl around the wire in the direction of the magnetic field. When viewed from the top, the fingers wrap in an anti-clockwise direction. Therefore, the magnetic field lines form concentric circles around the wire in the anti-clockwise direction as seen from the top.
Source: Chapter 12, Section 12.2.2 — Right-Hand Thumb Rule
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Explanation
- Examiners expect you to: (1) state the answer clearly first, (2) apply the rule step-by-step (thumb = current direction, fingers = field direction), and (3) relate it to the viewpoint (from top).
- A common mistake is confusing "current towards you" with clockwise — remember: anti-clockwise when current comes toward you (like a screw rule).
- Mentioning "concentric circles" earns credit as it shows understanding of the field pattern around a straight wire.