1. The problem statement, all variables and given/known data http://www.ph.qmul.ac.uk/~phy210/Ec2.pdf Question. 3) Alright I'm just going over things again so I'm ready for year 2 (this is year 1 question). I already know the method of answering (take a small part dE of the line, form an question of it's electric field on P, intergrate over the length L). http://www.ph.qmul.ac.uk/~phy210/ECAns2.PDF There's the answers, I don't understand why, when he also stated that all x-direction forces will cancel due to symmetry, and then says dE(y) = dEcos(theta) <-- isn't that the x-component of the field? I was intending to use sin(theta) until I saw he done that. Is this because when intergrated we end up with sin(theta)? Why do we use this process? Thanks!