Barlow's wheel was an early demonstration of a homopolar motor, designed and built by English mathematician and physicist, Peter Barlow in 1822.[1] It consists of a star-shaped wheel free to turn suspended over a trough of the liquid metal mercury, with the points dipping into the mercury, between the poles of a horseshoe magnet. A DC electric current passes from the hub of the wheel, through the wheel into the mercury and out through an electrical contact dipping into the mercury. The Lorentz force of the magnetic field on the moving charges in the wheel causes the wheel to rotate. The presence of serrations on the wheel is unnecessary and the apparatus will work with a round metal disk, usually made of copper.[2]
- "The points of the wheel, R, dip into mercury contained in a groove hollowed in the stand. A more rapid revolution will be obtained if a small electro-magnet be substituted for a steel magnet, as is shown in the cut. The electro-magnet is fixed to the stand, and included in the circuit with the spur-wheel, so that the current flows through them in succession. Hence, the direction of the rotation will not be changed by reversing that of the current; since the polarity of the electromagnet will also be reversed."
- (Excerpt taken from the 1842 edition of the Manual of Magnetism, page 94)[3]
It is used as a demonstration of electromagnetism in physics education. Because mercury is toxic, brine is sometimes used in place of mercury in modern recreations of the experiment.
- ^ on Peter Barlow in the Encyclopedia of geomagnetism and Paleomagnetism By David Gubbins, Emilio Herrero-Bervera ISBN 1-4020-3992-1, ISBN 978-1-4020-3992-8 (pp 44)
- ^ Barlow's wheel, electric motor. YouTube. Oct 25, 2013.
- ^ "Full text of "Davis's Manual of Magnetism: Including Also Electro-magnetism, Magneto-electricity, and Thermo ..."". archive.org. 1842.