Two positively charged identical metal spheres A and B have their centres separated by a distance of 
, as shown in the figure below.
The variation with distance 
from the centre of A of the electric field strength 
due to the two spheres, along the line joining their centres, is represented in the graph below.
State the radius of the two spheres.
The charge on sphere A is 
. Determine the charge 
on sphere B. Assume that spheres A and B can be treated as point charges at their centres. Explain your working.
Sphere B is removed. Use information from (b) to determine the electric potential on the surface of sphere A.
.
.
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