Magnetic Properties Simulation
Example 5.1: Magnetic Properties Exploration
(a) What happens if a bar magnet is cut into two pieces: (i) transverse to its length, (ii) along its length?
Solution: In either case, one gets two magnets, each with a north and south pole.
When you cut a magnet, each piece becomes a new magnet with its own north and south pole. This happens because magnetic fields are continuous and form closed loops - they cannot terminate at a point.
(b) A magnetised needle in a uniform magnetic field experiences a torque but no net force. An iron nail near a bar magnet, however, experiences a force of attraction in addition to a torque. Why?
Solution: No force if the field is uniform. The iron nail experiences a non-uniform field due to the bar magnet. There is induced magnetic moment in the nail, therefore, it experiences both force and torque.
The net force is attractive because the induced south pole (say) in the nail is closer to the north pole of magnet than induced north pole.
(c) Must every magnetic configuration have a north pole and a south pole? What about the field due to a toroid?
Solution: Not necessarily. True only if the source of the field has a net non-zero magnetic moment. This is not so for a toroid or even for a straight infinite conductor.
A toroid's magnetic field is completely contained within its windings, with no distinct north or south poles.
(d) Two identical looking iron bars A and B are given, one of which is definitely known to be magnetised. How would one ascertain whether or not both are magnetised? If only one is magnetised, how does one ascertain which one?
Solution: Try to bring different ends of the bars closer. A repulsive force in some situation establishes that both are magnetised. If it is always attractive, then one of them is not magnetised.
In a bar magnet the intensity of the magnetic field is the strongest at the two ends (poles) and weakest at the central region. This fact may be used to determine which is the magnet.
