WEBVTT 00:00:00.080 --> 00:00:02.766 This is College Physics Answers with Shaun Dychko. 00:00:03.180 --> 00:00:06.460 The force on a charge moving in the presence of a magnetic field 00:00:06.826 --> 00:00:10.986 is the charge in Coulombs times its velocity in meters per second 00:00:10.986 --> 00:00:13.640 times the magnetic field strength times sine of the angle 00:00:13.640 --> 00:00:15.706 between the velocity of the magnetic field. 00:00:16.426 --> 00:00:21.126 And we can solve for B by dividing both sides by qv sine theta. 00:00:25.540 --> 00:00:29.453 And so the magnetic field strength is the force divided by qv sine theta. 00:00:29.940 --> 00:00:34.746 So that's 1.7 times ten to the minus 16 newtons divided by the elementary charge 00:00:34.746 --> 00:00:36.193 which is the charge on a proton, 00:00:36.193 --> 00:00:39.260 because we are told that this cosmic array consist of a proton. 00:00:39.586 --> 00:00:41.860 So that's 1.6 times ten to the minus 19 Coulombs 00:00:42.306 --> 00:00:45.953 times five times ten to the seven meters per second times sine 45 00:00:45.953 --> 00:00:48.286 which is the angle between the velocity of the magnetic field. 00:00:48.606 --> 00:00:53.140 This gives a magnetic field strength of 3.01 times ten to the minus five Tesla. 00:00:54.920 --> 00:00:57.566 Now, the magnetic field strength of the earth 00:00:57.566 --> 00:01:00.613 is about five times ten to the minus five Tesla. 00:01:00.906 --> 00:01:05.666 And I say approximately equal because this magnetic field strength really varies 00:01:05.666 --> 00:01:07.666 depending on where your position is around the earth. 00:01:08.593 --> 00:01:13.766 And so we'll take the magnetic field we determined in part a and this is part b. 00:01:14.553 --> 00:01:16.966 And we'll take the magnetic field we determined in part a 00:01:16.966 --> 00:01:19.853 and divided by magnetic field of the earth in order to compare them. 00:01:20.206 --> 00:01:22.460 And we have three times ten to the minus five 00:01:22.460 --> 00:01:24.986 divided by five times ten to the minus five which is 0.60. 00:01:25.453 --> 00:01:29.186 So this means that our magnetic field that we calculated is 60 percent that of 00:01:29.486 --> 00:01:32.160 what is generally accepted to be the field strength of the earth 00:01:32.513 --> 00:01:36.713 and since this number is approximately can change, depending where you are. 00:01:37.106 --> 00:01:41.226 This means yes, our answer in part a is consistent with the earth's magnetic field.