Class 12 Physics - Chapter Magnetism and Matter NCERT Solutions | A sample of paramagnetic salt contains 2
A sample of paramagnetic salt contains 2.0 x 1024 atomic dipoles each of dipole moment 1.5 x 10-23 J T-1. The sample is placed under a homogeneous magnetic field of 0.64 T, and cooled to a temperature of 4.2 K. The degree of magnetic saturation achieved is equal to 15%. What is the total dipole moment of the sample for a magnetic field of 0.98 T and a temperature of 2.8 K? (Assume Curie's law)
Number of atomic dipoles, n= 2.0 × 1024
Dipole moment of each atomic dipole, M= 1.5 × 10 - 23J T - 1
When the magnetic field, B1= 0.64 T
The sample is cooled to a temperature, T1= 4.2°K
Total dipole moment of the atomic dipole, Mtot= n × M
= 2 × 1024× 1.5 × 10 - 23
= 30 J T - 1
Magnetic saturation is achieved at 15%.
Hence, effective dipole moment, 
When the magnetic field, B2= 0.98 T
Temperature, T2= 2.8°K
Its total dipole moment = M2
According to Curie's law, we have the ratio of two magnetic dipoles as:
Therefore, 10.336 J T-1 is the total dipole moment of the sample for a magnetic field of 0.98 T and a temperature of 2.8 K.
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