1. The problem statement, all variables and given/known data The points A,B,C are the vertices of an equilateral triangle, of side L. Two equal positive charges q are at A and B. A)Find the electric potential at C assuming V=0 at infinity B) Give the expression for the work necessary to bring a positive charge Q from infinity to C C)Write the expression for the work necessary to assemble the system of 3 charges, consisting of two charges q at A and B and a charge Q at C Consider the system of three charges. By differentiating the elctric potential,determine the electric field E at the midpoint between the two charges q. Consider now a system of 2 charges, a point charge q>0 at (x,y,z) = (a, 0 , 0) and a point charge -q/2 at (-a,0,0)Show that the quipontential surface V=0. ie. with the same potential than at infinity is a spherical surface. Determine the centre and the radius of the sphere. 2. Relevant equations 3. The attempt at a solution OK, I can do all the homework sheets, but these exam questions are killing me :-(, heres my attempts:# We have a triangle, with 2 positive charges and one unknown charge. If the unkown is positive we lose energy and if negative we gain energy. Possible pairs q1 q2 q2q3 q1q3 (I've divided by half already) I assume that we use something simliar to [tex]\int E.da[/tex]= Qinternal/Eo or we use the superposition principle, and add A and B together. using coloumbs law. E=k qi, q2 / r^2 In the first case, I have no idea. IN the second case, I think r^2 is just length A and length B so: E=k. q ^2 A.B Is this horribly wrong as I believe it is? For part B. I use phi=qi over 4 pi Eo Rij along with W=qphi to figure out. U= q1 q2 over 4 pi Eo r12 in which case we have U= q^2 over 4 pi Eo (2 (sqrt(half c^2 +D^2)) Part C I have no idea, Do we use the previous formula in some manner? Part D du/dr = q1q2/ 4pi Eo r^2 From there, I have no idea, would r be half AB? Part E Sorry :-( So yeah, this is quite shameful really, didn't expect not to be able to do any of this paper's B section!