# GRE solution still begs a question

1. Oct 5, 2013

### Kidphysics

1. The problem statement, all variables and given/known data

http://whoisntdavidrinaldi.com/physics/split.png [Broken]

2. Relevant equations

AxB=C

3. The attempt at a solution

I understand that the beam splits, but why does it not split horizontally? If I hold my index finger to the page with my middle finger up then my thumb is either left or right..

Last edited by a moderator: May 6, 2017
2. Oct 5, 2013

### jfizzix

Since the beam of hydrogen atoms electrically neutral, the Lorentz force law doesn't come explicitly into play. It is the magnetic dipole moments of the hydrogen atoms which determine which way the beam deflects.

Because the magnetic field is oriented vertically, the torque on the hydrogen atoms is such as to align their magnetic moments vertically (or at least precess about the vertical axis. However, because this magnetic field is not constant over the length of each atom, the atoms experience a net force as well, deflecting them either upward or downward depending on their magnetic moments.

Since a hydrogen atom in its ground state is equally likely to be spin-up or spin-down, we see the beam deflected into two equally intense halves.

3. Oct 5, 2013

### Kidphysics

i want to delete this post

4. Oct 5, 2013

### jfizzix

I'm sorry if my answer was unsatisfactory, but isn't that overdoing it?

5. Oct 5, 2013

### Kidphysics

No your answer was perfect, I responded but re-read your post and it answered the question I thought I had. Not knowing how to delete my post I just edited my answered follow up question to "id like to delete this post"

the answer was great, I thank you

6. Oct 6, 2013

### HallsofIvy

Staff Emeritus
Please do NOT delete threads after they have been answered. Others have the same questions and can learn from the answers.

7. Oct 7, 2013

### Staff: Mentor

As Halls said, it is our policy to not delete posts after they have received help. And if you do so yourself, you could receive an infraction for it.