What would happen if one cut the lines of magnetic force?
Armed with a practical knowledge of all that had yet been achieved in electromagnetism, Faraday began, in August 1831, ten days of intensive work at the Royal Institution which had a revolutionary effect. Ever since 1825 he had been querying whether an electric current passing through a conductor could not induce an electric current in a neighbouring conductor. On 29 August 1831 he succeeded in doing this with a 6 in. diameter iron ring, round which were wound five coils of copper wire, three on one side of the ring and two on the other. One of these coils was connected to the voltaic pile and the other to a galvanometer. The moment that the current in the battery was started, a transitory current appeared in the galvanometer in the opposite direction.
Figure 35. Faraday's Induction Coil - the first electrical transformer and one of the most treasured possessions of the Royal Institution. It consists of a soft iron ring around which were wound five cells of copper wire.Faraday then proceeded to prove that the lines of magnetic force could be cut, and a current induced, by simply rotating a copper disc by hand between the poles of a powerful electromagnet. This second fundamental discovery is the principle of the dynamo; it was soon applied in practice in the form of a number of small power-driven electric generators although a good many years elapsed, and numerous improvements had to be made, before they became very efficient. In 1841 power-driven multipolar machines were employed in Birmingham for the electroplating of copper articles and by 1858 a generator for electric light had been installed in the North Foreland Lighthouse.