[Bill Nettles] I simply want to make sure that I'm not having a brain freeze. I was working through some MasteringPhysics test bank questions and came across a couple of simple ones that I disagree with their answers.
Here are the paraphrased versions, with essential information:
1) An extensive sheet of a conductor carries charge density of 5 uC/mm^2 (u = micro). What is the electric field strength 9 mm from the conductor?
I got 5.6 x 10^11 N/C. They got half of that. I used density/epsilon0 because it's a conductor. It looks like they used density/(2*epsilon0).
2) A uniform electric field is 5 N/C r-hat. How much work is done on an electron which moves 6 m along a line tilted 30 degrees wrt r-hat.
I get +/- 26 eV depending on whether you move "with" or "against" the field. The question wasn't clear as to whether the field is doing the work, or another agent is moving the charge at a constant speed. In any case, they got 10 eV.