Question
A current through a horizontal power line flows in east to west direction. What will be the direction of magnetic field at a point directly below it when viewed from east end?
NDA
General Ability
General Science
2025
NDA 2025 (Phase 1)
NDA General Ability Question (2025) — Solution
Options
- A. Clockwise in a plane perpendicular to the wire
- B. Anti-clockwise in a plane perpendicular to the wire
- C. Clockwise in a plane of parallel to the wire
- D. Anti-clockwise in a plane of parallel to the wire
Answer
A. Clockwise in a plane perpendicular to the wire
Step-by-step solution
The current flows from East to West. When viewed from the East end, the current is flowing away from the observer. According to Maxwell's right-hand thumb rule, if the thumb points in the direction of the current (away from the observer), the curled fingers indicate the direction of the magnetic field lines. The fingers curl in the clockwise direction. Thus, the magnetic field lines form closed loops in the clockwise direction in a plane perpendicular to the wire. Answer: Clockwise in a plane perpendicular to the wire
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