Question
Explain diamagnetism and diamagnetic material.

Answer

→Simple explanation of dia-magnetism :
Electrons in an atom orbiting around nucleus possess orbital angular momentum. These orbiting electrons are equivalent to current carrying loop and thus possess orbital magnetic moment.
Diamagnetic substances are the ones in which the resultant magnetic moment in an atom is zero. When magnetic field is applied, those electrons having orbital magnetic moment in the same direction slow down and those in the opposite direction speed up.
This happens due to induced current in accordance with Lenz's law.
Thus, the substance develops a net magnetic moment in direction opposite to that of applied field and hence repulsion.
This is a simple explanation of diamagnetism.

Image
Fig. shows a bar of diamagnetic material placed in an external magnetic field. The field lines in it are repelled and field inside the material is reduced.
In most cases, this reduction is slight, being one part in $10^5$.
When placed in a non-uniform magnetic field, a diamagnetic substance experiences net force from stronger to weaker field and tends to move from high to low field. Which means they experience repulsion.
Some diamagnetic materials are bismuth, copper, lead, silicon, nitrogen (at STP), water and sodium chloride.
Value of $\chi$ (magnetic susceptibility) is negative $(-1 \leq \chi<0)$ for diamagnetic materials.

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