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Discovery of point-contact rectifier effect

This week, we will look at Karl Ferdinand Braun’s groundbreaking work in electric conductivity

November 23, 2015 01:04 pm | Updated November 10, 2021 12:31 pm IST

Professor Braun in his Laboratory

Professor Braun in his Laboratory

In 1909, Karl Ferdinand Braun shared the Nobel Prize in Physics with Guglielmo Marconi, “in recognition of their contributions to the development of wireless telegraphy.” Braun’s contributions, however, extended to fields other than wireless telegraphy and he is even believed to be responsible for the birth of semiconductor electronics. It is this discovery, his first groundbreaking work that he did in 1874, which we will be looking into this week.

Born at Fulda (in Germany) in 1850, Braun was the fourth child of Johann Conrad and Franziska Braun. After attending a Gymnasium (high school) for schooling in his teens, he enrolled himself at the University of Marburg, where he took courses in mathematics and chemistry. Before long, however, he shifted to physics and earned his PhD from the University of Berlin under the supervision of Professor George Hermann Quincke.

So when Quincke was appointed as Professor at the Wurzburg University, Braun followed him and worked as a graduate assistant. And it was here, when his research activities were focussed on problems of electric conductivity, that he made his first big discovery.

The rectifier effect Braun was studying the characteristics of electrolytes and crystals that conduct electricity. While probing a galena (lead sulphide) crystal using the point of a thin metal wire, Braun noticed that the current flowed freely only in one direction.

In a paper titled “Ueber die Stromleitung durch Schwefelmetalle” [About the conduction of current through metal sulphides], submitted on November 23, 1874 to Annalen der Physik and Chemie, Braun described the discovery of the rectifier effect. This property exhibited at the point of contact is referred to as the point-contact rectifier effect.

Even though Braun was looking for a method to establish electrical contact with minerals for his investigation of electrolysis, his research led him to point-contact rectifier effect, the foundation of solid-state electronics.

Electronic devices called diodes perform this kind of rectification. The Fleming valve that we looked at last week, was the first such practical device. Devices that use the point-contact rectifier effect perform the same function using semiconductor properties rather than thermionic properties.

Put into use Braun patented this work of his only decades later, when practical applications became much more obvious. It was used as a signal detector in a crystal radio set during the advent of radio in the early 20th century.

In 1897, Braun invented the cathode-ray tube, also known as Braun tube, which later became an integral part of the television receiver. Braun went on study the deviations from Ohm’s law and investigated oscillations of electrical rods and springs, while accepting a series of teaching positions in Germany.

Braun’s interest in wireless telegraphy enabled him to produce a sparkless antenna circuit that allowed Marconi to conduct the first transatlantic wireless transmission in 1901. It is for this reason that Braun is best remembered for his works with Marconi, which, as stated earlier, also won him the Nobel Prize.

Reach the writer at ganesh.a.s@thehindu.co.in

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