How to find a radius of a circular ring from a given equation

[raz23]

Homework Statement

There wasn't a figure given. All that was given was that the figure is a circular ring. Theta is the angle between the electric field direction and a unit vector normal to the surface area of the ring. Flux versus costheta was plotted and a slope was found to be m = 0.172. E = 220.

Homework Equations

ϕ=EAcosΘ

The Attempt at a Solution

I took the tan^-1 of 0.172 and then the cos of 9.76 and threw 9.76 for ϕ and .99 or the cos of 9.76 for theta and then divided 9.76 by .99. I thought the area was pi r². I multiplied 220 by pi and then divided that answer by 9.86 or 9.76/.99. And then took the square root of that. Is this correct? I'm thinking it's not.

 

[clementc]

Wouldn't the gradient of the line, m, just represent EA? And you know E already!