Tungsten Filament
Definition and meaning of Tungsten Filament in chemistry.
A tungsten filament is a thin coiled wire of tungsten metal (W) used in incandescent light bulbs to produce visible light when heated to high temperatures by electric current.
In more detail
Tungsten is the preferred choice for filaments because it has the highest melting point of any metal, approximately 3,422°C (3,695 K). When electric current passes through the filament inside an incandescent bulb, joule heating (resistive heating) rapidly raises the wire's temperature to 2,500-3,000 K. At these extreme temperatures, the glowing wire emits thermal radiation across the entire visible spectrum and beyond, producing the characteristic warm white light of incandescent bulbs. Tungsten's exceptionally low vapor pressure at high temperatures prevents significant evaporation, though gradual sublimation continues to thin the wire until it eventually fractures.
Key facts
| Chemical formula | W |
|---|---|
| Melting point | 3,422°C (3,695 K; highest of all metals) |
| Filament operating temperature | 2,500-3,000 K |
| Field | Inorganic Chemistry |
A typical 60-watt incandescent light bulb contains a tungsten filament approximately 60 centimeters in length (coiled very tightly to save space) that operates at approximately 2,800 K, producing approximately 800 lumens of visible light output.
Frequently asked questions
Why tungsten instead of other metals?
Tungsten has the highest melting point of any metal and the lowest vapor pressure at high temperatures, making it the dominant practical choice for sustained incandescent light production without melting or rapid evaporation.
Why do incandescent bulbs eventually fail?
The tungsten filament gradually sublimes (evaporates from solid directly to gas) at its high operating temperature, progressively thinning until it fractures. This typically occurs after 1,000-2,000 hours of use.