What is so special about the combination e/m ? Why do we not simply talk of e and m separately ?

Explanation

The motion of electron in electric and magnetic fields are governed by these two equations `1/2 mv^(2) = eV or Bev = (mv^(2))/r`
In these equations , e and m both are together i.e there is no equation in which e or m are alone . So, we always take e/m