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 0 × 104 N C–1, h = 1