00:01
Right, hello, in this question we're told that we have three -point charges on the y -axis, and we're given their charge values, the bottom -most one is negative, and they are separated by a distance of 8 centimeters between each of them.
00:12
We're asked in part a to find the electric potential energy of the configuration of the fixed three -point charges, which are the three that we've discussed so far.
00:19
So our total electric potential energy is going to be our electric potential energy from 1 on 2, plus our electric potential energy of 1 on 3, plus our electric potential energy of 2 on 3.
00:33
We know that electric potential energy is kq1q2 over r squared, so this is going to be r1, and it's not squared, my mistake, just kq1q2 over r, so we can expand that out into these other terms as well.
00:49
And then all we've got to do is plug in values.
00:51
Note, we're going to plug in negative for q2 because it is creating a negative electric potential energy by virtue of being negative.
01:00
So when we plug this in, we're just going to keep that sign in there.
01:04
I'm going to factor out the k, but i'm just going to plug everything else in.
01:07
I'm also going to factor out a 10 to the negative 9th times 2, or squared rather, because i have that in all of the terms, that's just so i don't have to write times 10 to the negative 9th six times.
01:20
And if i do that, i'm going to get an electric potential energy of negative 3 .60 times 10 to the negative 4th joules.
01:28
And what this means with the negative sign is that this is a configuration that wants to collapse together, and so to keep it apart, it would take positive work, and so we have this negative value here...