Question

Why is the effect of spin and magnetic moment of proton neglected

Answer 1

Spins of proton and electron are equal. But the magnetic moments are inversely proportional to the mass of the particle. ... Other is when net contribution of electron magnetic moment is zero. Then nuclear magnetic moment does matter (althought the effect is small).

Answer 2

That's because a proton doesn't have a magnetic moment as much as an electron.

Magnetic moment, as you may already know, is inversely proportional to the mass of electron or a proton, given by the relation:

μ=e2mL

Where μ is the magnetic moment, e is the charge, m is the mass and L is the angular momentum, which is quantized.

So, if me is the mass of the electron and mp is the mass of the proton-

Then, μe∝1me and μp∝1mp.

Here ∝ is the proportionality symbol.

Where μe and μp are the magnetic moments of an electron and a proton respectively.

Since the mass of a proton is approximately 2000 times larger than the mass of an electron, the magnetic moment of electron will be 2000 times larger than the magnetic moment of a proton.

Mathematically represented as,

μe≈2000μp