A solid metal sphere, of radius 
, is insulated from its surroundings. The sphere has charge 
. This charge is on the surface of the sphere but it may be considered to be a point charge at its centre, as illustrated in the figure below.
Define capacitance.
Show that the capacitance 
of the sphere is given by the expression
The sphere has radius 
. Determine, for this sphere,
the capacitance,
the charge required to raise the potential of the sphere from zero to 
.
.
.
