1. The problem statement, all variables and given/known data A semicircle of radius a is in the first and second quadrants, with the center of curvature at the origin. Positive charge +Q is distributed uniformly around the left half of the semicircle, and negative charge -Q is distributed uniformly around the right half of the semicircle. What is the magnitude and direction of the net electric field at the origin produced by this distribution of charge? Express your answer in terms of Q, a, and constants. 2. Relevant equations dq=λdL dE=kdq/a^2 3. The attempt at a solution I picked some random section (Θ up from the negative x-axis) on the left half of the semicircle and labeled it as dq with the length adΘ. I set dq=QadΘ and then dE=kQdΘ/a. Since the vertical components will all cancel, I focused in on the horizontal component and said dE_x=(kQdΘ/a)cosΘ. Since cosΘ=x/a at my point dq, I said dE_x=kQxdΘ/a^2. I know I'll have to pull out the constants and integrate dΘ over the interval ∏/2 to ∏, but how to I get rid of the x? Integrate it over 0 to a? Wouldn't I also need a dx? I originally thought it was a constant, but I can't leave my final answer in terms of x.