When an aluminum ring is placed on ring launcher so that it surrounds the coil,

Question

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.] I'd really appreciate it if you could include this "essential feature" my Professor is looking for in order for me to receive full credit. I've attached a picture showing the figures. Thank you in advance!

Explanation / Answer

When the AC-current was turned on, the emf generated in the Aluminum ing 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 n 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.

EMF, e =-d(phi)/dt .

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