Test: Classification Of Magnetic Material - Mechanical Engineering MCQ

Magnetic materials are the materials which can behave as magnets. When these materials are kept in an external magnetic field, they will create a permanent magnetic moment in it.

Magnetism originates from magnetic moment of the magnetic materials due to the rotational motion of the charged particles. When an electron revolves around the positive nucleus, orbital magnetic moment arises.

Magnetic lines of force are defined as the continuous curve in a magnetic field. The tangent drawn at any point on the curve gives the direction of resultant magnetic field at that point.

The magnetic lines of force which originate from North Pole to South Pole doesn’t end there itself. They are supposed to continue through the magnet and reach the North Pole from where they started and forms a closed loop. Such lines are called magnetic lines of induction.

The residual magnetism can be completely removed from the material by applying a reverse magnetic field. Hence coercivity of magnetic material is the strength of reverse magnetic field which is used to completely demagnetise the material.

 In a diamagnetic material, the electron orbits are more or less random, and mostly all the magnetic moments are cancelled. Similarly all the spins are almost paired. Hence the net magnetic moment in the diamagnetic material is zero.

The diamagnets are called weak magnets because there is no permanent dipole moment. Their net magnetic moment is zero.

Critical temperature is the temperature at which properties like magnetism changes. When the temperature is less than critical temperature, diamagnetic material becomes normal magnet.

Magnetic susceptibility is positive for paramagnetic material. It is given by Curie-Weiss law, Susceptibility = C/(T-θ)
Where, C = Curie constant
T = Absolute temperature
θ = Curie temperature

Critical temperature is the temperature at which properties like magnetism changes. When the temperature is less than critical temperature, diamagnetic material becomes normal magnet.