Tungsten filament lamp

Question: Can you explain the use of tungsten in the filament lamp? Why isn't the tungsten a good conductor? The books always refer to tungsten as a high resistance material.

Answer:

Have a look at the following web site:
http://www.tungsten.com/mtstung.html for a very useful table of the properties of tungsten.

The very high melting point of tungsten (3140^oC) compared with something like steel (1700^oC) or copper (1356^oC) means that it can withstand the high temperatures needed to give out sufficient light. The temperature of the filament in a light bulb is some 1800^oC.
It has a very low vapour pressure which means that even at high temperatures the light bulb is not filled with tungsten vapour.
It also has a very high tensile strength at the temperatures in the bulb. This makes it well able to withstand the thermal shock when the light bulb is switched on.
Important properties therefore: low vapour pressure, high tensile strength, high melting point.

Tungsten is not a 'good' conductor for two reasons:
(a) fewer free conduction electrons than, say, copper
(b) a large amount of electron scattering from the tungsten lattice.