00:01
Okay, so during chapter 27, problem 51.
00:03
It says in a mass spectrometer, germanium atoms have a radii of curvature equal to 21, 21 .6, 21 .9, 22 .2, and 22 .8 centimeters.
00:19
It says the largest radius corresponds to, so the largest radius corresponds to an atomic mass of 76 atomic units.
00:28
What are the atomic masses of the other isotopes? so the magnetic force on the ions causes them to move in a circular path, path, and our mass spectrometer.
00:40
So the magnetic force, qvv, is the centripetal force in v squared over r.
00:47
So if we rewrite this for m, this is qbr over v.
00:55
So now we can write the ratio of the mass over the radius, and this is equal to qb over v, and we know that this is going to be constant, because the mass is constant, and the radius is constant.
01:19
But we know the ratio is going to be constant.
01:22
So if we set m over r, then can now be 76 units over 202.
01:33
0 .8 centimeters and this is our ratio that all of these have to satisfy.
01:42
So if we're looking for the mass for 21 centimeter radius, this is just given by 76 u over 22 .8 times 21.
01:59
If you plug that in, this is 70 atomic units...