A charged metal sphere is isolated in space. Measurements of the electric potential 
are made for different distances 
from the centre of the sphere. The variation with distance of the potential is shown in the graph below.
Use the graph to determine the electric field strength, in 
, at a point where 
. Explain your working.
The charge on the sphere is 
. Use the graph to state the electric potential at the surface of the sphere.
.
.
