Q.
The mean free path of conduction electrons in copper is about 4×10−8m. Find the electric field which can give, on an average, 2eV energy to a conduction electron in a block of copper.
Mean free path d=4×10−8m,E=?
Energy of electron =2eV F=eE
Work done on electron when it moves through distance d=eED.
This work done is equal to the energy transfered to the electron, so ∴eEd=2eV Ed=2V E=d2V=4×10−82 =5×107V/m