- #1
21joanna12
- 126
- 2
I'm a bit confused about the electric field above a plate. First, I have come across the equation [itex]E=kQ[/itex] http://www.sparknotes.com/testprep/books/sat2/physics/chapter13section3.rhtml which in many ways makes sense to me because around a point the field would be proportional to [itex]1/{r^2}[/itex], and then for a line it would be proportional to [itex]1/{r}[/itex] etc, however I have not come across this formula anywhere else and am finding it hard to understand why moving away from the plate would not have any impact at all on the strength of the force on a changed partcle. Also, if this were the case then I would expect the field between two parallel plates to be [itex]E=2kQ[/itex] due to the principle of superposition. However I know from elsewhere that the E field between two parallel plates is [itex]E=V/d[/itex] and for a capacitor [itex]C=Q/V[/itex], and in the case of just air between the plates, [itex]C=\epsilon A/d[/itex], so putting that together I get that [itex]E=kQ/r^2[/itex]...
Have I made a wrong assumption somewhere?
Thank you!
EDIT: Sorry, for the last part I used [itex]A=4\pi r^2[/itex] which probably will not apply here. In that case, I am not sure what to do for the last part...
Have I made a wrong assumption somewhere?
Thank you!
EDIT: Sorry, for the last part I used [itex]A=4\pi r^2[/itex] which probably will not apply here. In that case, I am not sure what to do for the last part...