DANB Radiation Health and Safety (RHS) Practice Exam

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What phenomenon is thermionic emission associated with?

  1. Vacuum within the tube

  2. Filament wire heated to incandescence

  3. Stream of electrons

  4. High-voltage current

The correct answer is: Filament wire heated to incandescence

Thermionic emission is the release of electrons from a heated material, typically a metal. When a filament wire is heated to incandescence, it reaches a temperature high enough to provide sufficient energy for the electrons to overcome the attractive forces holding them within the atomic structure of the filament. This process is fundamental to the operation of devices like vacuum tubes and cathode ray tubes, where the emitted electrons can be manipulated to produce electrical signals or images. The phenomenon requires a specific temperature threshold to be met, which is why the filament needs to be heated to incandescence. At this point, a significant quantity of electrons is emitted into the vacuum surrounding the filament, allowing for various applications in electronic devices.

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