# Momentum of an electron

1. Nov 22, 2012

### DownQuark

When finding the momentum of an electron, would you use p=mγv or p=h/λ? It is a massive particle, so which one would you use?

2. Nov 22, 2012

### ZapperZ

Staff Emeritus
This cannot be answered without context. The momentum for electron in a material is different than finding it in a particle accelerator. So which one do you want?

Zz.

3. Nov 22, 2012

### DownQuark

Well what is the difference? And, which equation is for which case?

4. Nov 22, 2012

### ZapperZ

Staff Emeritus
One is a free particle and can be accurately described by classical physics. The other is a quantum mechanical situation.

Zz.

5. Nov 25, 2012

### Meir Achuz

$$p=mv\gamma$$ in any context. $$\lambda=h/p$$ for the wave function of an electron.

6. Nov 25, 2012

### HomogenousCow

Delends on the hamiltonian of the system, and there really exist no momentum eigenstates in reality, since they cannot be normalized.

If the above made no sense to you, the electron's momentum depends on the potential it is in, and even then you can only calculate the probability distribution, a momentum eigen state is not a physical state