How are electrons emitted from electrically heated metal filament?

Electrons are emitted from an electrically heated metal filament through a process called thermionic emission.

Here’s how it works:

  1. Heating the filament: When an electric current passes through the metal filament (often made of tungsten), the filament heats up. The energy from the electrical current increases the thermal energy of the metal’s atoms.

  2. Increased energy of electrons: As the temperature of the filament rises, the electrons in the metal gain more kinetic energy. The higher the temperature, the more energy the electrons acquire.

  3. Overcoming the work function: Every metal has a characteristic property called the work function, which is the minimum energy required for an electron to escape from the metal’s surface. When the electrons acquire enough energy from the heat (i.e., when their energy exceeds the work function), they can break free from the metal’s surface.

  4. Electron emission: Once the electrons have sufficient energy to overcome the work function, they are emitted from the filament into the surrounding space. This is the process of thermionic emission.

The emitted electrons are typically collected or directed in devices like vacuum tubes or cathode ray tubes, where they can be used for various purposes, such as in electron beams for displays or for amplifying signals in old-style electronics.

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