plotted in curve 2. 



ELECTROSTATICS 



The equation of this curve is 

 = de = _Q 

 dr r z 



13 



(b) Determine the potential and the potential gradient at any 

 point between two spheres A and B (Fig. 11) of radius R cm. if 

 the distance between their centres is D cm. and they have charges 

 of Q and Q respectively. This last condition means that all 

 the lines of dielectric flux which leave the sphere A fall on the 

 sphere B. 



FIG. 11. Potential and potential gradient between two spheres. 



At a point P on the line joining the centres of the two spheres 

 and at a distance of r cm. from the centre of A the potential due 



to the charge Q on A is , and that due to the charge Q on B 



is -=r ; the actual potential at P is, therefore, 



(15) 



