Question

A proton has spin and magnetic moment just like an electron. Why then its effect is neglected in magnetism of materials?

Answer 1

Spinning of a proton is negligible as compared to that of electron spin because its mass is very larger than the mass of an electron.

The comparison between the spinning of a proton and an electron can be done by comparing their magnetic dipole moment which can be given by

As we know that magnetic moment of a charged particle of charge e and mass m is Me = `(eh)/(4πme)` and Mp = `(eh)/(4πm p)`

As charge on proton and electron are equal in magnitude so

`M  oo 1/m` or `M_e/M_p = m_p/m_e`

As the mass of proton is 1836 times as of electron, so magnetic moment of proton

`M_p = M_e/m_p m_e = (M_e * m_e)/(1836  m_e)`, `M_p = 1/1836` of `M_e`

So magnetic moment of proton is `1/1836` times of electron, so can be neglected.