ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
High-current diode. This is the type of diode found in a vacuum tube, and consists of a set of electrodes separated by a vacuum. One electrode is positively charged, and the other is negatively charged. When current flows through the negative electrode (cathode) electrons are emitted by thermionic emission and flow to the anode. As heat is only applied to the cathode, the flow only takes place in one direction. This one-way flow is the basic principle of a diode. Modern diodes use semiconducting materials.
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