Electric Flux through Planar Surfaces

AI Thread Summary
The discussion focuses on calculating electric flux through two perpendicular planar surfaces with given areas and a uniform electric field. The correct formula for electric flux is Φ = EAcos(Θ), where Θ is the angle between the electric field and the normal to the surface. The initial calculation for surface 1 was incorrect due to confusion over the angle used; it should be the angle with the normal, not the surface. The participant realizes their mistake and clarifies their understanding of the angle's significance in the formula. The conversation concludes with a resolution of the confusion regarding the angle in the electric flux calculation.
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Homework Statement



The drawing shows an edge-on view of two planar surfaces that intersect and are mutually perpendicular. Surface 1 has an area of 1.2 m², while surface 2 has an area of 3.5 m². The electric field E in the drawing is uniform and has a magnitude of 246 N/C.

Image:

http://img513.imageshack.us/img513/9947/physicspf4.jpg

What's the electric flux through surface 1? What about surface 2?

Homework Equations



\Phi = EAcos\Theta

The Attempt at a Solution



For #1, I attempted to do 246*1.2*cos(55°), which is incorrect at 169.3197 Nm²/C.

What exactly am I screwing up here?
 
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If the field is perpendicular to the surface then flux is just EA. From this we conclude that the angle in your formula is the angle that the field makes with a normal to the surface, not the angle it makes with the surface.
 
Dick said:
If the field is perpendicular to the surface then flux is just EA. From this we conclude that the angle in your formula is the angle that the field makes with a normal to the surface, not the angle it makes with the surface.

Yeah, I was thinking things through and got my angles a bit mixed in the process, as you can see.

Got it now - thanks.
 
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