00:01
So according to this exercise there is this very long cable with two parallel lines and these two lines they carry a current of 80 .5 ampers and okay the current goes in opposite actions inside these two current lines and and these lines and these lines are located at the they cross the the y axis in this right -handed system they cross the lines cross the the y -axis at a position on the left with the coordinate y equals minus a and on the right with y coordinate with y coordinate equal to a this time and a equals to 7 .6 meters okay and we want to find out the magnetic field the magnetic field are a specific observation location a specific point a which is approximately about here with with coordinates minus 2 comma minus 2 .9 .0 in meters always and because because of the zero z coordinate.
01:35
We understand that this this a point is exactly on the same plane with these very long lines.
01:45
Okay, it is very important that we're talking about very long wire, very long lines because this immediately indicates which formula we need to use and this is the formula.
01:59
This is the formula that we need to use this an approximation formula when for the magnitude of the magnetic field of a wire indicates that the length of the wire is much much much larger than the dimensions and the radius of the wire this is this is what we mean by this condition that the length of the wire is much much larger the radius of the wire.
02:32
Okay, so the formula leads us new knot over four pi times times two times the kind over r.
02:48
Now this new over four pi is a typical constant that we encounter in magnetism and magnetostatics in a way.
02:58
It equals 10 to the minus seven the the exact units not important anyway.
03:05
Okay, this is the current.
03:06
Now we have to be a little bit careful with this simple here.
03:09
This is r, okay, the relative position vector, the relative distance, but it's the if we want to be precise, it's the it's the perpendicular distance, it's the perpendicular distance from the wire for a specific observation location okay so if let's say we choose another observation location here the relative distance the perpendicular distance from the wire this is something i'm into remember okay and this is the magnitude and in order to find out the direction the direction now of the magnetic field all we need to do is use the right hand rule and one can immediately see that the direction.
04:02
If, as an example, if the current goes that way, let's say to the left, the magnetic field goes down.
04:10
Okay, we have, again, we have two wires with the electric, excuse me, the current going in opposite directions.
04:21
The magnetic field, using the superposition principle, is just the vector.
04:29
We can find out the...
04:30
The net magnetic field by adding the two contributions, the contribution did from the left wire and the left line and the contribution from the right line.
04:44
Okay.
04:45
Now if one if one uses the right hand rule, one can see that the contribution from the from the left line goes down the magnetic field due to you to the left line goes down and it's exactly the same again for the right line the kind goes to the positive x direction and using the right handle we can see that again direction due to the right line it's again going towards the negative z direction to down as we see from here.
05:46
Okay, so we use this formula to write down the magnitude of each of the contributions and using the right handle we deduced the direction of the magnetic field.
06:05
Okay, this is the magnitude and this is the direction...