Given below are two statements:
Statement I : For diamagnetic substance, -1 ≤ χ < 0, where χ is the magnetic susceptibility.
Statement II : Diamagnetic substances when placed in an external magnetic field, tend to move from stronger to weaker part of the field.
In the light of the above statements, choose the correct answer from the options given below

Solution

Physics sir · 4 steps

Diamagnets push back on the field a little, so χ is negative but can never go below -1.

1. What diamagnetism does. In a diamagnetic material the induced magnetisation points opposite to the applied field. So M = χ H with χ < 0.
2. Lower limit on χ. The permeability is μᵣ = 1 + χ, and μᵣ cannot be negative. So χ ≥ -1. The value χ = -1 is the perfect diamagnet, a superconductor, which expels the field completely.

   μᵣ = 1 + χ ≥ 0 ⇒ -1 ≤ χ < 0

3. Motion in a field. Because the induced moment opposes the field, the energy is lower where the field is weaker. A diamagnetic sample is therefore pushed from the stronger part of the field towards the weaker part. Statement II is true.
4. So. Statement I gives the correct range and Statement II gives the correct behaviour. Both are true, which is option (a).

The idea to keep. Diamagnetic: -1 ≤ χ < 0, moves from strong to weak field. Paramagnetic: small positive χ, moves from weak to strong field. Ferromagnetic: very large positive χ.

Answer from the NTA final answer key. Solution by PrepWiser.