You should always first start by looking up the definition of a distribution you are interested in. In this case, that is all it takes. Find the definition of the F distribution and you will have your answer.
If X1 and X2 have a chi-square distribution with v1 and v2 degrees of freedom respectively, and they are independent, then I can say that Y~F(v1,v2) is an F distribution if Y=(X1/V1)/(x2/v2)..
I hope that this helps you