====== Eddy Currents In A Spinning Pie Plate ======

{{tag> eddy_currents electricity_and_magnetism induction lenz newton's_third_law located}}

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===== Description =====

Consists of an aluminum pie plate balanced on the tip of a pencil. A magnet is used to induce eddy currents in the plate and spin the plate.

===== Purpose =====

Demonstrate the induction of [[wp>eddy current|eddy currents]]. Demonstrate induced current/ magnetic fields. Demonstrate Lenz's law/ Faraday's law. Show that Newton's third holds, and the 'drag' experienced by the magnet (and shown by the [[demonstrations:5_electricity_and_magnetism:5k_electromagnetic_induction:magnets_through_copper_tube:start|magnet drop through copper tube demo]]) also translates to rotation of the disk.

===== Apparatus =====

  * Large aluminum pie plate/ serving plate
  * Pencil
  * [[demonstrations:9_equipment:lab_stands:start|Lab stand]] 
  * [[demonstrations:9_equipment:magnets:start|Large Neodymium magnet]]   

===== Setup =====

  - Tape the pencil to the top of the lab stand so that the sharpened point points upwards.
  - Place the plate on top of the pencil. There should be a small divot in the middle so it should stay. 
  - Ensure the pie plate is balanced. You can slightly bend the edges to adjust the balance. 
  - Hold the magnet about an inch above the surface of the plate and start making circles centered on the plate. 
  - You should now see the plate slowly begin to rotate in the same direction as the magnet.

===== Notes =====
The strength of this effect is mediated by a few things: 
  * The conductivity of the material. Copper would produce a stronger effect, but aluminum is still fairly conductive. A greater conductivity means the currents set up by the changing magnetic field will be stronger and therefore produce a greater force. 
  * The strength of the magnetic field (the size of the magnet / the proximity of the magnet). A greater magnetic field will produce a larger change in flux and therefore a greater force.
  * The speed of the magnet. A greater speed means there'll be a larger change in flux and therefore a bigger force. 


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| **Location** | O2 |
| **Maker** | Unknown |
| **Current State** | Working |
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