00:01
In this problem on the topic of magnetism, we are told that a lightning bolt can transfer 10 koolams of charge in 2 microseconds.
00:07
And if we model the bolt as a long current carrying wire, we want to find the magnetic field a meter from the bolt and the field a kilometer away.
00:16
We then want to compare these fields to the earth's magnetic field and then compare the fields in part a with the magnetic field that is produced by a typical household current of 10 -ampiers in a very long wire at these same distances.
00:28
We want to know then how close we would have to get to the wire for the magnetic field to be the same as the field produced by the lightning bolt at a kilometer from the bolt.
00:41
So for part a, the field ammeter away from the lightning strike is given by b, which is mu -naut times i over 2 pi times the distance r.
00:55
And we can write this as mu -naut and replace the current i by delta q over delta t, where delta q is.
01:02
The change in the charge over delta t which is the change in time so this is mu not delta q over 2 pi r delta t so putting in our values this is 4 pi times 10 to the minus 7 tesla meters per ampere which is mu not times a charge of 10 kuloms over 2 pi times a distance of one meter multiplied by a time of 2 times 10 to the minus 6 seconds.
01:47
This gives the field a meter away from the lightning strike to be one tesla.
01:53
And this is 20 ,000 times the earth's magnetic field.
02:10
And next for part b, or rather for part a still, but calculating the magnetic field a kilometer away from the lightning strike, we have b equal to mu not using the same equation, mu not delta q over 2 pi r delta t...