Ruhmkorff coil - definition

The Ruhmkorff Coils is a type of spark inductor, belonging to the class of interrupter induction transformers, which is used to generate a high impulse voltage from a low-voltage direct current source. This device was developed in the mid-19th century by German designer Heinrich Ruhmkorff, based on earlier work by William Sturgeon and Nicholas Callan. Its primary use was to power discharge tubes and generate sparks in experiments with electricity and vacuum.

The construction of the Ruhmkorff coil is based on two windings - a primary with a small number of turns and a secondary containing tens of thousands of turns of thin wire. Both windings are wound on a common core made of soft iron, usually in the form of rods grouped in a package. Coils' operation is based on the phenomenon of electromagnetic induction. The rapid interruption of current in the primary winding - realised by means of a mechanical interrupter - causes an alternating magnetic field, which induces high-voltage pulses in the secondary winding. In order to increase efficiency and to protect against arcing, an extinguishing capacitor was often used in the circuit.

The Ruhmkorff coil was widely used in physical experiments, as well as in wireless telegraphy, X-ray tubes and as an ignition element in internal combustion engines, before it was superseded by more advanced Instrumentation. Today, it remains mainly a historical and teaching object, used in demonstrations in electromagnetism.

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