Experiment of Arago’s Rotations with Easy obtainable materials


 Purpose of this article

Arago’s rotations know as Induction motor principle is summarized in this article.
And simple Experiment method is introduced.

Principle about Arago’s rotations 1

Japanese motor manufacturer Nidec Corporation explains Arago’s rotations as follows.

When Disc made from Copper or Aluminum is put between Magnets and Magnets are moved,
Eddy current is generated and Disc is also moved in same direction of magnets
due to Force generated by Eddy current.


It is attention point that Copper and Aluminum are nonmagnetic material and different from ferromagnetic material like iron and nickel.
As for Normal magnet, there is characteristic which attract ferromagnetic material and does not attract nonmagnetic material.
(However Neodymium magnet known for having strong adhesive force attract Alminum)

In fact, the principle of Arago’s rotation is not adhesive force of magnet.

The principle of Arago’s is explained in Next Chapter.

Principle about Arago’s rotations 2

Principle of Arago’s rotations is explained as below with the situation which the column shape magnet is located above aluminium board.

1.Magnet is moved from left to right.
Upper is S pole and Lower is N pole.

2.Magnetic field lines run from the N pole and Right side of magnet generates upward direction magnetic field line which prevent from increasing downward magnetic field due to Faraday’s electromagnetic induction law.
Left side of magnet also generates downward direction magnetic field line which prevent from decreasing downward magnetic field.

3.According to Right handed screw rule, Counter-Clockwise eddy current is generated on Right side Aluminum board relative to magnet.
Clockwise eddy current is also generated on Left side Aluminum board relative to magnet.

Above Items 1 to 3 is shown in Next Figure.


4.Eddy current is generated on Aluminum board in Right direction Relative to Magnet Moving direction.

5.Electric magnetic force in same direction of magnet moving is generated in Aluminum board according to the basis of Fleming’s left-hand rule because Magnetic field and Eddy current effect Aluminum board.
(Thumb:Mechanical force, Fore finger:Magnetic field, Middle finger:Electric current)

Above Items 4 to 5 is shown in Next Figure.

Experiment of Arago’s Rotations with Easy obtainable materials

You can confirm that Arago’s rotations that is the principal of Induction motor with easily obtainable material as below.

・A piece of Aluminum Foil
・Clear file folder (Any thin plate do as long as clear)

Fill a dish with water and Float A piece of Aluminum Foil on it.

Clear filde folder is covered with dish and Draw a circle with Magnet above the Aluminum Foil piece.
Then the piece is moved in the same direction of magnet moving.

This experiment movie is uploaded to youtube and refer to the following.


Posted by Gin