00:01
This is a nice little real -world example that gives us a mass spectrometer where we have germanium atoms with radii of curvature in a magnetic field of different values.
00:17
So i won't draw them all here, but this is just a schematic for what we're looking at physically.
00:24
And the different radii are r equals 21 centimeters, r equals 21 .6 centimeters, r equals 21 .6 centimeters, r equals 21 .9 centimeters, and finally, r equals 22 .8 centimeters.
00:49
Meters.
00:51
And we know that the largest radius corresponds to an atomic mass of 76 u, so atomic mass units, and we want to know the atomic masses of all the other isotopes.
01:14
So this really isn't something that's too tricky to figure out because we know that the force, which i'll right over here.
01:30
Qvb is equal to the centripetal, the force from the centripetal acceleration due to the circular motion.
01:45
So this equivalency is going to let us get an expression for the mass, which is qbr, all on v, which is the velocity, but we can actually move, get this in terms of a mass ratio, which is going to simplify things.
02:12
So if you write m over r is equal to q times b over v, which is the velocity, this is actually a constant.
02:32
So q is the atomic charge, which depends on the number of protons, which since it's germanium, they all have the same number of protons, so that's constant.
02:44
The magnetic field is constant...