1. The problem statement, all variables and given/known data Two half-rings of charge of opposite polarity are brought together at the origin (so that the rings create a full circle against the y- and z-axis. Each half-ring has a charge of magnitude Q and radius a. Derive the net electric field at point P, located on the +x axis a distance d from the centre of the two half-rings. 2. Relevant equations Not sure. 3. The attempt at a solution I really have no idea how to work this out from what we learned in lecture; "electric field of a ring of charge".. Help, please!