Concepts Of Physics MCQ Edition [Volume 2]PhysicsPermanent Magnets
A circular loop of radius a carries an electric current i . A very long bar magnet is positioned such that its north pole is located at the centre of the loop. The magnetic field produced by the magnet at any point on the periphery of the wire is B . The force acting on the wire is
Options
- Avery nearly 2 a i B perpendicular to the plane of the wire
- Ba i B along the magnet
- Czero
- D2 a i B in the plane of the wire
Correct answer
A. very nearly 2 a i B perpendicular to the plane of the wire
Step-by-step solution
The north pole of a very long bar magnet acts approximately as a magnetic monopole. When placed at the centre of the circular loop, the magnetic field B produced by it at any point on the periphery of the wire is directed radially outward. Let the current element of the circular loop be d l . Since the wire is circular and the field is radial, the angle between the current element d l (which is tangential) and the magnetic field B is 90^ . The magnetic force on the small current element is given by: d F = i(d l B )