Q1. [1] medium thorough-understanding
The magnetic field at the centre of a current-carrying circular loop is directed perpendicularly into the plane of the loop. If you reverse the direction of the current in the loop, which of the following correctly describes the resulting field at the centre?
(A) It remains directed into the plane of the loop, but doubles in magnitude.
(B) It is directed perpendicularly out of the plane of the loop.
(C) It becomes zero because the contributions from opposite sides cancel.
(D) It rotates to lie within the plane of the loop.
- A It remains directed into the plane of the loop, but doubles in magnitude.
- B It is directed perpendicularly out of the plane of the loop.
- C It becomes zero because the contributions from opposite sides cancel.
- D It rotates to lie within the plane of the loop.
Generated by claude-sonnet-4-6 · 2026-06-26 01:11 · grounding rag
Model Answer
(B) It is directed perpendicularly out of the plane of the loop.
Reversing the current reverses the direction of the magnetic field at the centre, as confirmed by the right-hand thumb rule.
Explanation
By the right-hand thumb rule, the direction of the magnetic field at the centre of a circular loop depends on the direction of current. Reversing the current reverses the field direction — from into the plane to out of the plane (or vice versa). The magnitude stays the same; only direction changes. Examiners expect students to apply the right-hand thumb rule correctly here.