why filament become hot
Answers
Answer:
The filament of an electric bulb glows because of the heating effect of electric current. As the current passes through the bulb it heats the filament which gives off light. The filament then heats up and becomes red-hot as a result of this it begins to glow, turning electrical energy into light energy.
Answer:
In vacuum tubes and gas-filled tubes, a hot cathode or thermionic cathode is a cathode electrode which is heated to make it emit electrons due to thermionic emission. This is in contrast to a cold cathode, which does not have a heating element. The heating element is usually an electrical filament heated by a separate electric current passing through it. Hot cathodes typically achieve much higher power density than cold cathodes, emitting significantly more electrons from the same surface area. Cold cathodes rely on field electron emission or secondary electron emission from positive ion bombardment, and do not require heating. There are two types of hot cathode. In a directly heated cathode, the filament is the cathode and emits the electrons. In an indirectly heated cathode, the filament or heater heats a separate metal cathode electrode which emits the electrons.
A tungsten filament in a low pressure is mercury gas discharge lamp which emits electrons. To increase electron emission, a white thermionic emission mix coating is applied, visible on the central portion of the coil. Typically made of a mixture of barium, strontium, and calcium oxides, the coating is sputtered away through normal use, eventually resulting in lamp failure.
