00:01
We want to find the magnitude of the magnetic field that a power line with a current of 95 amps is making on the ground.
00:09
And so the ground is 8 .5 meters below the line here.
00:13
So we just treat this as an infinitely long line of currents.
00:20
And so we know the magnetic field is just mu not times i over 2 pi r, where r is the distance to where we're looking at the field.
00:30
So mu not times 95 amps over 2 pi times our distance which will be 8 .5 meters.
00:43
And this will come out to be 2 .2 times 10 to the minus 6 teslas.
00:50
And then we're asked to compare this to earth's field.
00:53
So we just do this value divided by the magnetic field of the earth, which is 0 .5 times 10 to the minus 4 teslas.
01:01
And so we do that and we get 0 .047.
01:08
So that means that on the ground, the field from this wire is about 4 .5 % that of earth's field.
01:17
And so then in part b, we're asked to find at what distance would the field actually cancel with earths.
01:24
So first off, i think we're supposed to assume that earth's field is pointing in the north direction here.
01:30
And so north here is into the page, south...