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An isolated solid metal sphere A of radius 
has charge 
, as illustrated in the figure below.
A point P is distance 
from the surface of the sphere. Determine an expression that includes the terms and 
for the electric field strength 
at point P.
A second identical solid metal sphere B is now placed near sphere A. The centres of the spheres are separated by a distance 
, as shown in the figure below.
Point P lies midway between spheres A and B. Sphere B has charge 
. Explain why
the magnitude of the electric field strength at P is given by the sum of the magnitudes of the field strengths due to each sphere
the electric field strength at point P due to the charged metal spheres is not, in practice, equal to 
, where is the electric field strength determined in (a).
