00:01
So this question is quite fiddly.
00:04
So i would make sure you go through it quite slowly when you do it.
00:09
So we get this diagram here which is we have six charges which i've label 1 to 6.
00:15
Charge 1 is plus 7 q charge 2 is plus 3 q plus charge 3 is plus 5 q plus charge 4 is minus 5 q and charge 6 is plus 7 cube.
00:28
We have sides of d on all the 4.
00:31
Sides in between charges and therefore the the vertical distance to p is d over two in each directions and so the distance from the sides to p is the distance the distance from the corners to p is is going to be marked by z and move down the second and from the bottom to the center so x as we said is d y is d over 2 and therefore z is equal to d squared plus d squared over 4 which is 5 d squared over 4 root 5 over 2d now the most important thing we can do here obviously this is a bit of a mess so we need to simplify this what we notice is at 1 and a 6 we've got two opposite things so they're exactly equal to each other side by side which means that the potential from each of these will cancel each other out.
01:31
So the one and the six you don't have to worry about.
01:35
For the two and the five, this is minus three q, this is plus three q.
01:40
So this is effectively like having a charge of plus six q over here.
01:44
And similarly for three and four we have a plus five q here and a minus five q here...