Question

A paramagnetic gas consists of atoms each with a dipole moment of $1.5\times 10^{-23}J/T$. Temperature of the gas is $27^{\circ }C$ and its number density is $2\times 10^{26}{m}^{-3}$. What is the maximum magnetisation of the sample possible when placed in an external field ?

• A. $1\times 10^{3}A/m$
• B. $2\times 10^{3}A/m$
• C. $3\times 10^{3}A/m$
• D. $4\times 10^{3}A/m$

Answer 1

Answer: (C)

Dipole moment of each atom, M = $1.5\times 10^{-23}$ J/T
Magnetic field. B = 2T
Number density $n=2\times 10^{26}{m}^{-3}$
Temperature of gas T = 27${}^{\circ }$C = 300 K
Maximum magnetisation, M${}_{max}=nM=2\times 10^{26}\times 1.5\times 10^{-23}=3\times 10^3$ A/m
Magnetisation actually achieved by sample is much less than M${}_{max}$ because due to thermal agitation all dipoles do not align in direction of magnetising force.