{"id":4739,"date":"2024-07-25T10:33:40","date_gmt":"2024-07-25T15:33:40","guid":{"rendered":"https:\/\/commons.princeton.edu\/josephhenry\/?page_id=4739"},"modified":"2024-07-25T14:37:58","modified_gmt":"2024-07-25T19:37:58","slug":"faraday-unipolar-generator","status":"publish","type":"page","link":"https:\/\/commons.princeton.edu\/josephhenry\/faraday-unipolar-generator\/","title":{"rendered":"Faraday Unipolar Generator"},"content":{"rendered":"

Tesla Pratt, <\/span>7\/25\/24 – <\/span>Professor Littman<\/span><\/p>\n

Objective:<\/strong> I will study Michael Faraday\u2019s lab notebook and diaries, and recreate his experimental procedures with the unipolar electric generator. I will design a simulation in COMSOL multiphysics to compare with calculated and experimental results from my recreation. An analysis of both calculated, simulated, and experimental data, I look to confirm Faraday\u2019s results with various configurations and tests with the homopolar generator.\u00a0<\/span><\/p>\n

In 1831, Faraday discovered electromagnetic induction by passing a magnet through coiled wire. He attached a galvanometer to the coil, and observed that moving his magnet through created a deflection in the needle. Curiously, this \u201cinduced current\u201d in the coil could only be observed when there was relative motion between the two bodies. If both were held in close proximity but without movement, no deflection occurred. <\/span>These experiments led Faraday to develop Faraday\u2019s Law: <\/span>E=-N<\/span>t<\/span>, which states that E (in volts) is equal to the change in flux of the system, over change in time. In other words, as the magnetic flux\/field changes in the system over a certain interval of time, electricity is produced.\u00a0<\/span><\/p>\n

Faraday saw this as an opportunity to produce electricity in a new way, and created the first electric generator \u2013 the faraday unipolar generator. In a diary entry from October 1831, Faraday details the physical configuration of the generator, and draws a sketch:<\/span><\/p>\n

Diary Entry <\/span>OCT. 28, 1831: \u201c99*. Made many expts. With a copper revolving plate about 12 inches in diameter and about \u2155 of inch thick, mounted on a brass axle. To concentrate the polar action two small magnets 6 or 7 inches long, about 1 inch wide and half an inch thick were put against the front of the large poles, transverse to them and with their flat sides against them, and the ends pushed forward until sufficiently near\u201d(Faraday\u2019s Diary VOL I, 381)<\/span><\/p>\n

\"\"<\/p>\n

How Current is Induced in the Plate:<\/strong><\/p>\n

Faraday summarizes the effects of rotating the plate through a magnetic field in another diary entry from November 1831 explaining that \u201cthe rotating plate is merely another form of the simpler experiment of passing a piece of metal between the magnetic poles\u201d. In both cases \u2013 disc and metal bar, currents of electricity are produced at right angles to the direction of motion (Eddy Currents) in the place where the magnetic poles cross the surface.<\/span><\/p>\n

 <\/p>\n

Model Replica: <\/b>Using parts we had on-hand in the Princeton MAE lab, I designed a replica model of Faraday\u2019s original experiment:<\/span><\/p>\n

\"\"\"\"<\/p>\n