Page "Thermionic emission" Paragraph 8

Edison built several experiment bulbs, some with an extra wire, a metal plate, or foil inside the bulb which was electrically separate from the filament, and thus could serve as an electrode.

He connected a galvanometer, a device used to measure current, to the output of the extra metal electrode.

When the foil was charged negatively relative to the filament, no charge flowed between the filament and the foil.

We now know that this was because the filament was emitting electrons, and thus were not attracted to the negatively charged foil.

In addition, charge did not flow from the foil to the filament because the foil was not heated enough to emit charge ( later called thermionic emission ).

However, when the foil was given a more positive charge than the filament, negative charge ( in the form of electrons ) could flow from the filament through the vacuum to the foil.

This one-way current was called the Edison effect ( although the term is occasionally used to refer to thermionic emission itself ).

He found that the current emitted by the hot filament increased rapidly with increasing voltage, and filed a patent application for a voltage-regulating device using the effect on November 15, 1883 ( U. S. patent 307, 031, the first US patent for an electronic device ).

He found that sufficient current would pass through the device to operate a telegraph sounder.

This was exhibited at the International Electrical Exposition in Philadelphia in September 1884.

William Preece, a British scientist took back with him several of the Edison Effect bulbs, and presented a paper on them in 1885, where he referred to thermionic emission as the " Edison Effect.

" The British physicist John Ambrose Fleming, working for the British " Wireless Telegraphy " Company, discovered that the Edison Effect could be used to detect radio waves.

Fleming went on to develop the two-element vacuum tube known as the diode, which he patented on November 16, 1904.