Tungsten Filament Heating Effects

Extract

The subject of SEM saturation was discussed on the microscopy list server and off list I was aslied why filaments burn out on the side leg Instead of at the tip. I have degrees in electronics technology and in chemistry as well as being a microscopist. So I investigated this subject and performed some experiments to verify my results.

According to Ohm's Law, one would expect that the highest resistance would be at a sharply bent V’ and that is where the filament would be expected to burn out. However, observations of the phenomenon show this is not where the filament burns out.