# Electric potential (need help with angle)

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1. Nov 10, 2014

### dmack15

1. The problem statement, all variables and given/known data
The electric potential of a region of space is V= 200 / sq root (x^2 + y^2), where x and y are in meters. What are the strength and direction of the electric field at (x,y) = (2m,1m)?

2. Relevant equations

3. The attempt at a solution
I took the negative derivative of V to find what the electric field would be.

Then i substituted in (2,1)
200(2)(5)^-3/2 x + 200(5)^-3/2
=35.78x + 17.89 y

im having trouble figuring out where the angle should be. i do this a lot.

if i take the arctan or tan-1 of Ey/Ex

i get an angle of 26.6 degrees. Now is that 26.6 degrees ccw above the x-axis??
im having trouble figuring out where the final electric field will end up.
when i looked at the signs of x,y theyre both negative in the problem which means it would be quadrant 3.
even when i do 360-26.6 it ends in quadrant 4 which doesnt make sense

Please i dont need any help with the problem just with some help understanding the angle

2. Nov 10, 2014

### dmack15

nevermind the x and y components are both positive so it falls in quadrant I.