Question

By which of the following activities can a magnet lose its property?
A. Excess heating
B. Demagnetizing magnetic field
C. Sudden shock
D. All of the above

Answer 1

Hint: Recall that the behaviour of magnets is consistent with the domain theory of magnetism, where the material of the magnet is made up of small domains that encompass vibrating atoms pointing to a specific direction. Now, think of what would happen to the atoms in the so-called domains if they were subjected to intense heat induced vibrations or were exposed to a demagnetizing field or were subject to sudden impacts leading to shock propagation throughout the material of the magnet. This should help you arrive at the appropriate conclusion.

Complete step by step answer:
Let us begin by understanding the domain theory of magnets. It suggests that the volume of a magnetic material is made up of smaller elements called domains, each which contain a certain number of atoms whose magnetic axes are aligned in the same direction even in the absence of any external field. For a magnet, the all atoms in each domain are aligned in a specific direction.
Now, the atoms in a magnet are always in a state of vibration in random directions. These vibrations are created as a result of energy from normal temperatures. Excess heat causes these atoms to move more rapidly, disturbing the magnetic domains. If a magnet is heated beyond a point called the Curie temperature the heat will permanently disrupt the domain structure of the material and will lose all of its magnetization. As the atoms speed up, the percentage of domains having atoms pointed in the same direction decreases, which in turn weakens the magnetic force and eventually demagnetise entirely.
Now, if a magnet is exposed to a magnetic field that is sufficiently higher than its coercivity (which is the amount of magnetizing field intensity that is required to destroy the magnetism in the magnet) and of an opposite polarity, the magnet will get demagnetized either completely or to an extent, depending on the strength of the field applied.
Also, very sharp impacts can jostle the orientation of the atoms in the magnet by sending a shock through the material caused by dropping the magnet or by hitting it with a hammer. Since (permanent) magnets have no external field to guide the atoms to re-align themselves in the desired orientation, they will align back in random directions which will reduce the magnetization intensity of the magnet.
Thus, all three processes, i.e., excess heating, exposure to demagnetizing magnetic fields and sudden shock lead a magnet to lose its magnetic property.

So, the correct answer is “Option D”.

Note: Note that a magnet can also lose its magnetism over time, owing to factors besides the ones discussed above.
Like we mentioned, the atoms in a magnet are always in a state of randomly directed vibrations. These vibrations are created as a result of energy absorbed from normal room temperatures. With time, these vibrations change with changes in ambient/room temperature which subsequently randomizes the magnetic domain orientations, leading a magnet to lose its magnetic property.