Ncert Exercises & Solutions

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

Hint: The mass of the proton is much greater than the mass of the electron.

Step 1: 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:

M = \frac{eh}{4 πm} or M \propto \frac{1}{m} (∵ \frac{eh}{4 π} = constant)

∴ \frac{M_{p}}{M_{e}} = \frac{m_{e}}{m_{p}}

= \frac{M_{e}}{1837 M_{e}} (∵ M_{p} = 1837 m_{e})

\Rightarrow \frac{M_{p}}{M_{e}} = \frac{1}{1837} << 1

\Rightarrow M_{p} < < M_{e}

Thus, the effect of magnetic moment bf proton is neglected as compared to that of the electron.

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