An isolated metal sphere is charged to a potential 
. The charge on the sphere is 
. The charge on the sphere may be considered to act as a point charge at the centre of the sphere. The variation with potential of the charge on the sphere is shown in the graph below.
Use the graph above to determine
the radius of the sphere,
the energy required to increase the potential of the sphere from zero to 
.
The sphere in (a) discharges by causing sparks when the electric field strength at the surface of the sphere is greater than 
. Use your answer in (a)(i) to calculate the maximum potential to which the sphere can be charged.
.
.
.
