Homework Help: Electric Flux with angles

1. Jul 17, 2007

exi

1. The problem statement, all variables and given/known data

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 [Broken]

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

2. Relevant equations

$$\Phi = EAcos\Theta$$

3. 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?

Last edited by a moderator: May 3, 2017
2. Jul 17, 2007

Dick

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.

3. Jul 17, 2007

exi

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

Got it now - thanks.