Question

What is the function of filament?

Answer 1

Three functions of filaments in electronics are as part of a ‘cat’s whisker’ crystal radio detector; as a source of electrons for vacuum tubes, including electron microscopes and x-ray tubes; and as a heatable semi-blackbody for incandescent lighting. Crystal radios using actual crystals are a just ‘do it to show it can be done’ phenomenon (and is not the general use of the word filament in electronics), vacuum tubes have been mostly supplanted by solid state devices, and incandescent lighting is also being phased out. Their use is rapidly being limited to special applications that actually require a source of electrons.