# Electric field strength near a metal plate

Tags:
1. Feb 8, 2017

### jlmccart03

1. The problem statement, all variables and given/known data
A total charge of 21 μC is applied to a thin, 1μm square metal plate 72 cm on a side.

Find the electric field strength near the plate's surface, far from the edges.

2. Relevant equations
I think E = kq/r^2, but I really don't know.

3. The attempt at a solution
I am having a hard time figuring out where to start. I know I must find the electric field strength (i.e magnitude), but where do I begin and what do I do to find it. I just know that E = kq1q1/r^2, but there is no second charge so it must be kq1/r^2 correct? Do I use that or something else?

2. Feb 9, 2017

### BvU

No responses so far. Pressure's off if you've had your exam by now. Still want to address this one ?

3. Feb 9, 2017

### rude man

There is a simple formula giving the E field near the surface of a charged medium such as a metal plate. Very simple.

4. Feb 9, 2017

### jlmccart03

My exam is today, but I managed to figure this one out. First converting the units into the proper units that I wanted to use I figured that for a plane its q/2a^2 and thus I entered to the units in and divided that by epsilon naught. I got 2.3 MN/C

5. Feb 9, 2017

### BvU

Yes. My personal association is with the term Gaussian pillbox

A comment on the exercise: I miss the words 'uniformly distributed' ; that way good students easily get wrong-footed.