What process describes the boiling of electrons from the filament in a tube?

The process of boiling electrons from the filament in a tube is known as thermionic emission. This phenomenon occurs when the filament is heated to a high temperature, causing the thermal energy to impart enough energy to the electrons so that they can overcome the work function of the material and escape into the surrounding vacuum.

In thermionic emission, the key concept is the application of heat, which excites the electrons within the metal of the filament. As the temperature rises, the kinetic energy of the electrons increases until they reach a point where they can leave the metal surface. This process is crucial in devices such as vacuum tubes and cathode ray tubes used in early television technologies, where a stream of electrons is necessary for operation.

The other options involve different concepts. Photonic emission relates to the release of photons (light particles) rather than electrons. Electromagnetic radiation refers to waves of electric and magnetic fields spreading through space, which is not related to the emission of electrons from a heated source. Electron discharge typically refers to the movement of electrons through a medium but does not specifically describe the boiling-off process from a filament induced by temperature. Thus, thermionic emission accurately describes the boiling of electrons from a filament in a tube.