Ruhmkorffs

Ruhmkorffs, often referred to as Ruhmkorff coils, are a type of transformer used to produce high-voltage, low-current, high-frequency alternating current electricity. They were invented by the German physicist Heinrich Wilhelm Dove in 1850 and later significantly improved by the French electrical engineer Nicolas Callan in 1851, though they are primarily named after German instrument maker Heinrich Daniel Ruhmkorff, who commercialized and refined the design in the 1850s.

The basic principle of a Ruhmkorff coil involves two coils of wire wound around a common iron core. The primary coil has relatively few turns of thick wire, while the secondary coil has many thousands of turns of thin wire. An intermittent direct current is passed through the primary coil, which generates a changing magnetic field. This changing magnetic field induces a voltage in the secondary coil. Due to the large difference in the number of turns between the primary and secondary coils, a very high voltage is generated in the secondary. The spark gap across the secondary winding serves as a switch, causing the current to oscillate and break down, thereby creating the high-frequency output.

Ruhmkorff coils were crucial for early electrical experiments, particularly in the study of electricity and magnetism, and for the development of technologies such as X-rays and early radio transmission. They were capable of producing impressive electrical discharges, often used for public demonstrations of electrical phenomena. While largely superseded by more modern technologies like solid-state electronics for most applications, they remain historically significant and are still used in some niche scientific and educational contexts for their ability to generate high voltages.