Question

In a permanent magnet at room temperature -

A. Magnetic moment of each molecule is zero.
B. The individual molecules have non-zero magnetic moments which are all perfectly aligned.
C. Domains are partially aligned.
D. Domains are all perfectly aligned.

Answer 1

Hint: Ferromagnetic atoms form groups which we call domains. Domains are responsible for the magnetic properties of the magnet. Permanent magnet is a special type of ferromagnets that retain the magnetic properties for a long time.

Complete answer:
Some materials can hold magnetic properties long after we remove the external effects. We call these materials permanent magnets. All the atoms are made of electrons which revolve around the nucleus. The fourth quantum number ‘s’ of the electrons is responsible for the magnetic property of materials.

Most of the materials do not possess the magnet property due to the orientation of these atoms. In regular materials, the atoms orient themselves in such a way that the effective magnetic moment becomes zero. Whereas, permanent magnets show the effects of magnetism at room temperature.

There are only four naturally occurring elements which can show the properties of permanent magnetism at room temperature. These materials are iron, nickel, cobalt, and gadolinium. They are called ferromagnetism. The magnetic property is due to the regions which we call domains. In these materials, the atoms form a group where the atoms arranged themselves in the same magnetic orientation.

A ferromagnetic material, which does not have any magnetic property, has all the domains arranged in such a way that the effective magnetic dipole is zero. When we apply an external magnetic field using another permanent magnet or current flow, the domains arrange themselves perfectly. The perfect orientation of the domains is responsible for the magnetism of permanent magnet.

So, the correct answer is “Option D”.

Additional Information:
There are two ways by which you can make a permanent magnet. These two ways are –
1) Using the magnetic field of another permanent magnet.
2) Using the magnetic field generated by a conductive coil which is carrying current.

Note:
Permanent magnets retain the magnetism due to a property called Hysteresis. When we remove the effects of the magnetic field, the domains do not reorient themselves. If we heat the material to a particular temperature, it loses the property of magnetism.