A point charge -q is placed at a distance d from an isolated...

A point charge -q is placed at a distance d from an isolated conducting plane. The field at a point P on the other side of the plane is a. directed perpendicular to the plane and away from the plane b. directed perpendicular to the plane but towards the plane c. directed radially away from the point charge d. directed radially towards the point charge

Transcript

00:01 Here we're going to find the electric field at a point, a distance, certain distance 2d, away from a conducting plane, and there is a charge plus q sitting on top of that conducting plane.

00:19 And the method we're going to use is a nice little trick called the method of images.

00:25 What that method relies on is that you're putting.

00:30 Potential in a region is unique as long as you have the potential specified on a boundary.

00:39 So i'm going to go ahead and pretend that we know that conductor plane is grounded so that we have a very unique potential sitting there.

00:50 And the idea is that as long as you do something to recreate the potential on the boundary, you're good to go.

01:00 So the idea is why where the image comes in is you can imagine an image charge.

01:11 It's not really there, but you can imagine it there of negative q.

01:17 And then everywhere along that conductor is equidistant from both charges, as long as you put that imaginary charge one distance away.

01:28 But the conductor everywhere along it is equidistant from those two -point charges, and so the potentials add up to zero everywhere along there.

01:47 And so you've kind of matched the uniqueness of that boundary.

01:53 But once you put that image charge there, then it is a simple matter to figure out the electric field at any point.

02:02 You so choose as long as it's in the region of the real charge off limits...

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