Question

A paramagnetic gas consists of atoms each with a dipole moment of $1.5\times10^{-23}\,J/T$. Temperature of the gas is $27^\circ C$ and its number density is $2\times10^{26}\,m^{-3}$. What is the maximum magnetisation of the sample possible when placed in an external field ?

• A. $1\times10^3\,A/m$
• B. $2\times10^3\,A/m$
• C. $3\times10^3\,A/m$
• D. $4\times10^3\,A/m$

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.