State the relationship between electric potential and electric field strength at a point.
Two parallel metal plates A and B are situated a distance 
apart in a vacuum, as shown in the figure below.
Plate A is earthed and plate B is at a potential of 
. A helium nucleus is situated between the plates, a distance x from plate A. Initially, the helium nucleus is at rest on plate A where 
.
The helium nucleus is free to move between the plates. By considering energy changes of the helium nucleus, explain why the speed at which it reaches plate B is independent of the separation of the plates.
As the helium nucleus (
) moves from plate A towards plate B, its distance x from plate A increases. Calculate the speed of the nucleus after it has moved a distance x = 0.40 cm from plate A.
and the potential difference 
:
at which the helium nucleus reaches plate B is independent of the separation 
of the plates.
from plate A is 
.
