About Electromagnetism
Faraday studied the magnetic field around a conductor canying a DC electric current, and established the basis for the electromagnetic field concept in physics. He discovered electromagnetic induction, diamagnetism, and laws of electrolysis. His inventions of electromagnetic rotary devices formed the foundation of electric motor technology, and it was largely due to his efforts that electricity became viable for use in technology.
An electric current is accompanied by a magnetic field. Wrap several turns of wire in a coil to amplify the effect. Insert an iron core to amplify it further.
Faraday wrapped two insulated coils of wire around an iron ring, and found that upon passing a current through one coil, a momentary current was induced in the other coil ('mutual induction'). He found that if he moved a magnet through a loop of wire, an electric current flowed in the wire. The current also flowed if the loop was moved over a stationary magnet. His demonstrations established that a changing magnetic field produces an electric field. Induction coils, transformers, and electric motors are based on these effects.
Delzenne's Circle is an apparatus for showing induced currents produced by rotation of a coil in the Earth's magnetic field. It is used to measure the magnitude and direction of the earth's magnetic field. The rotating coil is quickly flipped through 180 degrees, and the output is fed to a ballistic galvanometer. This device, with a long period of oscillation, measures the total charge delivered by the induced EMF; the charge is then proportional to the magnitude of the magnetic field threading the coil. The apparatus was devised by Charles Edouard Joseph Delzenne (1776-1866).
A Helmholtz coil is a device for producing a region of nearly uniform magnetic field. It is named in honour of the German physicist Hermann von Helmholtz. Useful for deflecting electron beams in cathode ray tubes (e.g. Teltron).
Barlow's Wheel was an early demonstration of a homopolar motor, designed and built by English mathematician and physicist, Peter Barlow in 1822. An electric current passes through the hub of the wheel to a mercury contact on the rim; this is contained in a small trough through which the rim passes Due to health and safety considerations brine is sometimes used today in place of mercury. The interaction ofthe current with the magnetic field of a U-magnet 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.