00:01
In this question, we have four long straight wires, labeled 1, 2, 3 and 4.
00:05
They overlap to form a square of side 2r as labeled here.
00:10
Each one carries a current equal to i.
00:13
What we want to find is the magnetic field at the centre of the square and compare it to what it would be at the centre of a circular loop, which has been drawn in red here with a radius of r.
00:23
So what we need to use is but the biosavir law to find the magnetic field.
00:28
This is shown here.
00:29
It states that the current in a long wire is equal to 2 pi r times the magnetic field over mu not.
00:38
So rearranged, we can see that the magnetic field due to a long straight wire is equal to mu nor i over 2 pi r.
00:46
So what we can do now is also say, looking at the right hand rule, the contribution from each of these wires is going to be out of the plane of the paper at the centre.
00:57
So the net field is going to be the sum of all of the individual fields.
01:02
So what we can say is that b net is equal to b1 plus b2 plus b3 plus b4...