Electric flux through the earth

[sashab]

Homework Statement

The Earth's radius is 6370 km . There is a downward-pointing electric field in the atmosphere above the Earth's surface, of average magnitude 140. N/C .

a) What is the flux of the electric field out of the Earth?
b) What is the charge on the Earth?

Homework Equations

\Phi=\vec{E}\bulletA

The Attempt at a Solution

I figured that this would be a simple problem of the electric flux through a sphere, so I thought if I used the above equation and by plugging in the area of the sphere I would get the right answer for a), but the computer is saying I'm incorrect. :( I got an answer of 7.13x10^16 N*m^2/C. I know that flux involves integration, but I'm only just starting to learn it so I don't know how to use integration in a problem like this yet. Any help would be really appreciated! Thanks

 

[Dick]

Homework Statement

The Earth's radius is 6370 km . There is a downward-pointing electric field in the atmosphere above the Earth's surface, of average magnitude 140. N/C .

a) What is the flux of the electric field out of the Earth?
b) What is the charge on the Earth?

Homework Equations

\Phi=\vec{E}\bulletA

The Attempt at a Solution

I figured that this would be a simple problem of the electric flux through a sphere, so I thought if I used the above equation and by plugging in the area of the sphere I would get the right answer for a), but the computer is saying I'm incorrect. :( I got an answer of 7.13x10^16 N*m^2/C. I know that flux involves integration, but I'm only just starting to learn it so I don't know how to use integration in a problem like this yet. Any help would be really appreciated! Thanks

That's a good try. Though you should say how you got it. The thing you might be missing is that flux can be either negative or positive. The question is asking for the flux "out of the Earth".

 

[sashab]

That's a good try. Though you should say how you got it. The thing you might be missing is that flux can be either negative or positive. The question is asking for the flux "out of the Earth".

Ohh okay I see where I went wrong. Thanks for the help!