State what is meant by electric field strength.
An isolated metal sphere A of radius 
is positively charged. Sphere A is shown in the figure below.
Electrical breakdown (a spark) occurs when the electric field strength at the surface of the sphere exceeds 
. Calculate the maximum charge 
that can be stored on the sphere.
A second isolated metal sphere B, also with charge 
, has a radius of 
. Calculate the additional charge, in terms of , that may be stored on this sphere before electrical breakdown occurs.
.
.
