Download Hollow charged conductors

The variation of electric field strength and electric potential for a hollow conductor
You can show by experiment that there is no charge inside a hollow charged conductor - all the
charge is on the surface. This means that the electric field inside the sphere is also zero and the
potential is constant. The variation of electric field intensity and the electric potential for a hollow
charged conductor is shown in the following graphs.
Electric field intensity
Electrical Potential
E
V
distance
distance
Example problem
The graph shows the variation of potential around a point charge in a vacuum.
Use the graph to calculate:
(a) the electric field intensity at d = 24 nm
(b) the size of the charge
assume (1/4 εo) = 9x109 Fm-1
(a) gradient of curve = 200/5x10-9 = 4x1010 Vm-1
(b) At d = 24 nm, V = 603 V therefore using VE = (1/4 εo)Q/d Q = VEd/(1/4εo) = 1.6x10-15 C
Breakdown field strength for an insulator
There will come a point where the insulating properties of an insulator break down if the potential
difference across it and hence the electric field strength within it is large enough. This is called the
breakdown field strength. The value of the breakdown field strength for dry air is in the region of
5x105 Vm-1.