# I Fermi-dirac integral

1. Mar 25, 2016

### arneet

• Thread closed due to being posted in two forum sections
i am completely lost. there is an integral in my textbook in fermi dirac statistics whose result is written directly and am not able to understand . it is .
on expansion by using the method of taylor's series the result should be
where u_f is such that function of u is zero for u greater than uf.
plz reply as soon as possible. thanks.

2. Mar 25, 2016

### Alpharup

I think this should have been posted in physics thread. Anyways, i will explain here...Assume u is greater than uf....so (u-uf) is so large...
so in 1+(exp(u-uf)/kT) can be approximated as (exp(u-uf)/kT)

The reciprocal of this term is (exp-(u-uf)/kT).

Hope this helps

3. Mar 26, 2016