Chapter 7, Problem 45R

To determine

To Explain: A bar magnet will attract an iron nail to either its north pole or its south pole, but it will attract another magnet to only one of its poles.

Explanation of Solution

Introduction:The domains of a magnetic material tends to align themselves according to the magnetic field lines of a nearby magnet.

The magnetic field of each atom of a magnetic material exerts a force on nearby atoms. These forces cause alignment of large groups of neighbouring atoms with their same magnetic poles in the same direction.

Theregions where magnetic poles of atoms are aligned are called magnetic domains. Because of the aligned magnetic poles of the atoms, the domain itself behaves like a larger magnet with a north pole and a south pole.

If an iron nail is attracted by a bar magnet, the domains of the nail tend to align themselves according to the bar magnet’s magnetic field. If it is near the north pole, the domains are so aligned that the south pole of each atom is towards the north pole of the magnet and so the nail is attracted by the bar magnet’s north pole. Similarly,if the nail is near the south pole, the domains are so aligned that the north pole of each atom is towards the south pole of the magnet and so the nail is attracted by the bar magnet’s south pole. Therefore an iron nail is attracted by both the poles of the bar magnet.

However, for another magnet, the magnetic field directionis already fixed, and so the bar magnet will attract this magnet to only one of its pole depending on which pole is towards it. If the two magnet opposite poles are towards each other, the magnet will attract, else repel.

Conclusion: The domains of the iron nail align themselves according to the magnet’s pole; but the bar magnet will attract another magnet to only one of its poles, because the other magnet’s poles are fixed.