# Homework Help: Effective mass question

1. Feb 25, 2007

### raintrek

1. The problem statement, all variables and given/known data

Calculate the effective mass for a free electron.

2. Relevant equations

3. The attempt at a solution

I know the above equation comes from, in the case of the free electron dispersion relation, .

However i'm not at all sure how to go about calculating it for a free electron, given that the two formulae are basically one in the same...

2. Feb 25, 2007

### Gokul43201

Staff Emeritus
Note the following minor correction: the free electron dispersion relation is $\epsilon = \hbar ^2 k^2 /2m_e$. What happens when you plug this into the expression for the effective mass?