Consider a rectangular cardboard having two holes P and Q through which a current carrying circular loop has been inserted as shown in the diagram.
Generated by claude-sonnet-4-6 · 2026-06-15 06:48 · grounding rag
Model Answer
(a) [Diagram to be drawn in answer sheet]
The magnetic field lines should be drawn as follows:
- Point 1 (near P): Concentric circles around the wire where it passes through hole P.
- Point 2 (centre of loop): Straight parallel lines through the centre of the loop (all pointing in the same direction).
- Point 3 (near Q): Concentric circles around the wire where it passes through hole Q (direction opposite to those at P).
(b) The intensity of the magnetic field at the centre of a circular loop depends on:
- The magnitude of current flowing through the loop (field increases with current).
- The number of turns of the coil (field is n times for n turns).
(c) Right-Hand Thumb Rule — To determine the direction of the magnetic field produced by a current-carrying straight conductor.
Source: Chapter 12, Sections 12.2.1 and 12.2.3
---
Explanation
- (a) The key point: at the centre of the loop, the arcs appear as straight lines (all contributions add up in the same direction). Near P and Q, the wire is straight, so field lines are concentric circles. Examiners want the contrast between straight-line field at centre vs. concentric circles near holes.
- (b) From the textbook: field depends on current AND number of turns. A common error is writing "radius/distance" — while valid in general, the textbook specifically highlights current and number of turns for the centre of a circular loop.
- (c) "Right-Hand Thumb Rule" is specifically mentioned for straight conductors. Don't confuse with Fleming's Left-Hand Rule (for force on conductor) or the Right-Hand rule for circular loops.