The acceleration of the electron is
ae  =  eE/me
where me is the mass of the electron Starting from rest, the time required by the electron to fall through a
distance h is given by  
2
2
e
e
e
h m
h
t
a
e E
=
=
For e = 1 6 × 10–19C, me = 9 11 × 10–31 kg,
     E = 2