Distribution of Charges Part A Calculate the magnitude of...

Distribution of Charges Part A Calculate the magnitude of the electric field at the origin due to the following distribution of charges: -q at (x,y) = (a,a), -q at (a,-a), +q at (-a,-a) and +q at (-a,a). Where q = 3.25 imes 10^{-7} C and a = 4.40 cm. Part B Set up an 8-point compass at the origin, where north points along the positive y-axis, such as that shown in the diagram to the right. What is the direction of the electric field at the origin created by the charge distribution given in the previous part? (for example, 'N', 'NE', etc., or if no net field enter 'NIL').

Transcript

00:01 Okay, in this problem, i have a set of four charges.

00:03 I made a picture of this, so let me show you a picture.

00:06 That will make it a life easier, i think.

00:09 Okay, so i've got these four charges, and three of them are positive.

00:17 So the blue ones here, these are all positive.

00:20 They all have the same magnitude, all four of the charges.

00:23 Just the one on the lower right -hand corner is negative, and that's the one colored in red.

00:30 And the square has a side link of 2 times a.

00:34 I'm going to tell you what a and q are in a minute.

00:38 The square is centered on the origin.

00:40 So, for example, this point here is that this is at equal negative a and a.

00:47 And this is at a and a.

00:51 And this is at a, negative a.

00:58 And then this point is negative a, negative a.

01:02 Okay.

01:03 So these are these four charges.

01:07 And then i have this angle.

01:09 And this angle you can see is equal to 45 degrees.

01:12 That actually cuts that 90 degree angle and a half.

01:16 That's pretty pretty easy to see.

01:18 But hopefully you get that.

01:21 Okay.

01:21 Now, so that's basically the setup here.

01:25 And what we're asked to do is to find the electric field at the origin here, right there in the center.

01:31 So we want to know what the e -field there is.

01:33 Now, i can write out just the expression for the electric field, but let me make a couple of points here.

01:40 So the electric field due to this charge down here points up and that way.

01:46 So up into the right.

01:48 And the field due to this charge down here points down and to the left.

01:53 And these have the same magnitude because they're the same distance from the center.

01:58 And they have the same magnitude of charge.

02:00 So this guy, the field due to this guy, cancels, this one, cancels this one.

02:08 So those two cancel.

02:09 So i don't have to worry about those two charges at all.

02:11 The only charges i have to worry about are these other two charges, the one up here in the upper left and the one here on the lower right.

02:19 Now here, this field is going down and to the right because that's a positive charge.

02:29 So it points from the direction of the charge to the field point.

02:35 Because this is a negative charge, this points from the field point in the direction of the charge.

02:42 So the field due to this guy here points down and to the right in the same direction as the first one.

02:50 So they have the same magnitude of charge.

02:53 So i don't really need to even calculate both of them.

02:56 I'm just going to calculate the field due to this guy right up here.

03:00 Put in there.

03:01 We'll call it, say, i'm making him green...

Question

Please give Ace some feedback