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184_notes:examples:week12_moving_coils_flux [2017/11/10 20:26] – [Solution] tallpaul | 184_notes:examples:week12_moving_coils_flux [2018/04/11 19:36] (current) – [Solution] pwirving | ||
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===Facts=== | ===Facts=== | ||
* The rings are oriented so that there is a magnetic flux through one due to to the other. | * The rings are oriented so that there is a magnetic flux through one due to to the other. | ||
+ | * There is only current in the first ring. | ||
===Lacking=== | ===Lacking=== | ||
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{{ 184_notes: | {{ 184_notes: | ||
====Solution==== | ====Solution==== | ||
- | Before any motion happens, we can look at the rings from a side view, and represent the magnetic field as shown below. The direction is determined using the [[184_notes: | + | Before any motion happens, we can look at the rings from a side view, and represent the magnetic field as shown below. In the side view it looks like current is coming out of the page at the top of the coil and going into the page at the bottom. The direction |
{{ 184_notes: | {{ 184_notes: | ||
- | When the rings begin to move towards one another, you can imagine that the second ring experiences an increase in magnetic flux, since the magnetic field is stronger closer to the ring with current. When we say the flux " | + | When the rings begin to move towards one another, you can imagine that the second ring experiences an increase in magnetic flux, since the magnetic field is stronger closer to the ring with current. When we say the flux " |
Since the flux is increasing, we expect the induced current in the second ring to oppose this increase. This requires for the induced current to produce a magnetic field pointing to the left. We can use the [[184_notes: | Since the flux is increasing, we expect the induced current in the second ring to oppose this increase. This requires for the induced current to produce a magnetic field pointing to the left. We can use the [[184_notes: | ||
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In fact, this induced current and resulting magnetic field from the second ring will actually cause a changing flux through the first ring that actually increases its currently momentarily. We are able to reconcile this with conservation of energy because even though the current increases in both rings, the resulting magnetic forces between them opposes their motion. | In fact, this induced current and resulting magnetic field from the second ring will actually cause a changing flux through the first ring that actually increases its currently momentarily. We are able to reconcile this with conservation of energy because even though the current increases in both rings, the resulting magnetic forces between them opposes their motion. | ||
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+ | {{youtube> |