# Ring launcher conceptual question

1. Apr 2, 2016

### Physicsnoob24

1. The problem statement, all variables and given/known data
When an aluminum ring is placed on ring launcher so that it surrounds the coil, it flies upward when a AC current is applied to the coil. This does not occur when the intact ring is replaced by a split ring (see below). Explain this in 3 sentences or less. Feel free to use as many diagrams and equations as you need in your explanation. [Warning: The standard explanation of this lacks any mention of an essential feature.]

2. Relevant equations

3. The attempt at a solution
This is my rationalization as to why this occurs:
When the AC-current was turned on, the emf generated in the Aluminum ring led to a current in it, which according to Lenz's Law, has to be in a direction such that its field cancels the one due to the ring launcher: so it is opposite in direction and since opposite currents repel, the ring flies off. When a split ring is used, since it is not a closed loop, there is no flux going through it is 0. Hence, there is no emf or current generated: so it does not fly off.

Did this go beyond the "standard explanation", as my Professor puts it? Or did I miss something "essential?"
I have uploaded a picture of the figure (if it helps at all). I can only receive partial credit if my Professor isn't completely satisfied with the answer so if I'm missing something, I would greatly appreciate it if anyone could help steer me in the right direction. Thank you so much!

File size:
42.9 KB
Views:
31
2. Apr 3, 2016

### Staff: Mentor

Currents do not repel. There is something else that repels something.
Going through what?
One of them is generated.

I don't know what exactly your prof means, but here is a question you did not answer: how does the ring know in which direction it has to go?