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physgirl
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Homework Statement
find electric flux that enters left hand side of a cone (with base radius R and height h). electric field penetrates the cone horizontally (cone is on a horizontal table).
Homework Equations
flux = surface integral of EdA
where E represents component of electric field normal to surface
The Attempt at a Solution
so that's the formula I got from my book... so I thought I had to find the integral of Ecos(theta)dA... since Ecos(theta) would be the component of E that's normal to slanted surface of the cone... and if I integrate with respect to A I get Ecos(theta)A... cos(theta) is h/sqrt(h^2+R^2)... area of cone (minus the base) is pi*R*sqrt(h^2+R^2)...
so I did... E*(h/sqrt(h^2+R^2))*[pi*R*sqrt(h^2+R^2)]/2
once I cancel out stuff, I get: E*(h)(pi*R)/2... 2piERh
however, the back of my book says the answer is ERh... why??