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**[SOLVED] Electric field in cartesian coordinates**

## Homework Statement

Suppose the electric potential is

V(r) = C1 /r + C2 cosθ /r^2

where (r, θ, φ) are the spherical polar coordinates for points in three dimensions.

[Data: C1 = 4.3 Vm ; C2 = 1.6 Vm^2 ]

(A) Determine the electric field at a point on the x axis, E(x,0,0) where x=0.3 m. Give the three Cartesian components of the field, (Ex,Ey,Ez).

## Homework Equations

r=sqrt{x^2+y^2+z^2}

θ=arccos(z/r)

E=-dV/dr

## The Attempt at a Solution

cos(θ) is zero since the z coordinate is zero, and cos(θ) is z/r. I find the derivative of 4.3/r at r = 0.3, and multiply it by -1 to get 47.778 V/m. I believe that the other coordinates would be zero, since the radius for both of them is zero. However, i don't get the right answer. What would the problem be?

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