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## Homework Statement

A disk with a radius of 0.6 m is given a uniform charge density of -7.2*10

^{-9}C/m

^{2}. The disk is in the xz plane, and centered at the origin.

A. What is the size and direction of the electric field at the point A, whose coordinates are (0m, 1.5m, 0m)?

B. You now add an infinite line with a uniform charge density of +400 pC/m

What is the position of the line if the electric field at point A now has a size of 100 N/C and points upward

**Relevant equations**

- ∫E(vector)*dA(vector)=q
_{enclosed}/( ε0)

- A
_{disk}=πr^{2} - A
_{Sphere}=4πr^{2} - σ=Q/A

- λ=Q/l

- ε0=1/(4πk
_{e})

_{ The Attempt at a Solution Part A. So I first made a sphere around point A as my gaussian surface. I next solved for Q=σA and used Q as my enclosed charge. Next, I got rid of the dot product in ∫E(vector)*dA(vector) by making it negative. My reasoning was that the surface charge density was - so the E would be opposite the dA(vector). The E is constant at all points of the sphere so I was able to bring the E out of the closed integral. Next I did ∫dA and got the ASphere=4πr2. So, my equation turned into -E(4πr2)=(Adisk)(σ)/(ε0). With algebra I solved for E and got E= 32.54. This doesn't seem like a correct answer and there seems to be some uncertainty in my method which doesn't seem correct. Part B. I cant seem to understand how I am able to find the position of the line with Gauss's law. I can find the length, but I cant seem to understand how to start this part.}[/sub]