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5K10.80 - Faraday's Disc

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5K10.80 - Faraday's Disc

Title5K10.80 - Faraday's Disc

​To demonstrate generation of DC voltage with the rotational motion of an electrically conductive disc in a plane perpendicular to a uniform static magnetic field.

Assembly Instructions

Attach a meter with a mV setting to the Faraday disc.  Using a 3M pad, clean the surface of the rotating disc to ensure there is a good connection between it and the brush commutator​.

Setup Time5
Operation Time5
Preview Time5
Operation Instructions

With the multimeter attached, spin the conductive disc in the direction indicated.  You should see a few milivolts generated by this apparatus.  Then switch the multimeter to the amp setting and observe the larger value of the current produced by this apparatus.​

NOTE:  This Faraday's Disc is NOT designed to be a motor and a generator due to the type of "brush" commutator that was used.

Demo on DimeNo
PIRA 200No
Export Instructions (if different)

Disk-type generator:  Also known as a unipolar generator, acyclic generator, or disk dynamo

One of the electrical contacts is near the axis and the other near the periphery. It has been used for generating very high currents at low voltages in applications such as welding, electrolysis, and railgun research.
In contrast to other types of generators, the output voltage never changes polarity. The charge separation results from the Lorentz force on the free charges in the disk. The motion is azimuthal and the field is axial, so the electromotive force is radial. The "brush" contact is an inefficient way to contact the disk due to the number of large losses that exist at the low voltages that are present.  Historically, mercury was used to provide constant contact, but due to the toxicity of mercury we do not use it.
When the magnetic field is provided by a perminant magnet, the generator works regardless of whether the magnet is fixed to the stator or rotates with the disc. Before the discovery of the electron and the Lorentz force law, the phenomenon was inexplicable and was known as the Faraday paradox.
Category5 Electricity and Magnetism
Subcategory5K - Electromagnetic Induction
Keywordsgenerator, faraday, disk,
Construction Information
Faraday's disc generator
banana cable
multimeter - voltage DC
camera - b&w