00:01
Here we'll be using kulom's law to calculate the net force on a point charge.
00:08
So kulom's law is a law about the force of interaction between two point charges.
00:18
And it is a vector relationship.
00:21
I usually like to think of it with absolute value of the two charges in the numerator with the electrical constant k, divided by the charge separation squared, and then a little unit vector, which you use repulsion attraction to determine.
00:42
Now, we are going to be finding the net force on a middle charge due to two others, and in order to do that, we just superpose forces from different interactions together.
01:01
So we will work on that.
01:05
Now, life is a little bit easy because we are in one dimension.
01:10
So we know that our situation is going to be forces only in the y direction, with positive y up and negative y down.
01:25
Like usual, i like to show a force diagram of the situation, just so i get the picture right.
01:32
So we are concentrating on charge three.
01:36
It has a force from the top charge that is repelling it, which we'll call f2.
01:44
It also has an attraction from the bottommost charge, also directed downwards, which will call f1.
01:57
Simply put, that is helping to figure out the little unit vector r -hat.
02:05
So in this case, both situations have negative y.
02:10
So let me figure out the magnitudes of those two forces, or the y components with the negative sign in front.
02:22
F2y, i will insert a negative, is k, q3, q22, absolute value.
02:38
And let's just pick out the separation.
02:41
The separation between them is 0 .4 meter squared.
02:47
Denominator.
02:50
It's important to write down k is a fundamental constant.
02:57
I usually like to use 8 .99 times 10 to the 9th in the si units, newton's times meter squared over kulom squared.
03:12
So now we can figure out one of these forces, okay, and a product of our two charges with an absolute value.
03:31
Here i am i am using the idea that a nano means the same as 10 to the minus 9...