(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A point charge q is held a distance d > a below the centre of a large spherical conductor of radius a. Show that, if the spherical conductor is earthed, the potential outside the sphere may be found by placing an image charge at a distance c=a^{2}/d from the centre of the sphere, and determine the charge stored on the spherical conductor.

(I CAN DO THIS PART OF THE QUESTION FINE)

Instead of being earthed, the net charge on the spherical conductor is now set to zero. Explain why, in order to represent the electric field outside the conductor an additional image charge must now be included inside the sphere, and determine the potential of the conductor.

2. Relevant equations

I found the image charge to have a charge -aq/d

3. The attempt at a solution

I can do the first part of the question fine. But I'm getting confused when we set the conductor to zero charge.

My reasoning for why we need an additional image charge is that ( I Think) the overall charge of all the image charges inside the conductor should now also be zero. Hence, we would need an image charge of +aq/d inside the sphere...

My intuition was to put it at a distance a^2/d in the opposite direction to the other image charge so it makes a dipole with it centred at the origin of the sphere... But I don't really no if this is right or if its justified.

I don't know how I can then calculate the potential easily without doing alot of trig and maths?

Thanks very much

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# Homework Help: Method of Images in Electrostatics

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