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Magnitude of electric field at a point 
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#1
Oct1012, 10:02 AM

P: 1

1. The problem statement, all variables and given/known data
A force of 5.7 N. is exerted on a 8.8 microCoulomb charge in a downward direction. What is the magnitude of the electric field (in N./C.) at this point? 2. Relevant equations E = (kel * abs(q)) / r^2\ E = Fel / q 3. The attempt at a solution 8.8 microcoulombs > 8.8e6 Coulombs At first I tried using: E = (8.99x9)(8.8e6) / r^2 But I didn't understand how I was supposed to find the radius. If it were a square, rectangle, triangle etc. and given some more information I could use trigonometry to determine the radius. The equation is for a point charge, though. I then used E = Fel / q and simply plugged and chugged to get the right answer. My question, though, is when do I use the E = Fel / q and when do I use the E = kq/r^2 equation? Is the point charge for when two points are being compared to each other and the E = Fel/q is for one item? 


#2
Oct1012, 11:48 AM

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P: 41,475




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