What metal are filaments in light bulbs made of?

• A. Tungsten
• B. Copper
• C. Aluminum
• D. Iron

Answer: (A)

Filaments in incandescent bulbs must stay solid and intact at extremely high temperatures long enough to glow and produce light. Tungsten is used because it has an exceptionally high melting point, about 3422°C, and a very low vapor pressure when hot, so it doesn’t evaporate away quickly. This combination lets a tungsten filament reach the bright, hot temperatures needed for visible light while keeping its shape and strength. It can also be drawn into a very fine wire and formed into a long, thin filament that can withstand the stresses of being coiled inside the bulb. The bulb’s interior is kept in vacuum or filled with an inert gas to reduce oxidation, since tungsten can form oxides at high temperatures in air. Metals like copper, aluminum, or iron melt or vaporize far sooner under those conditions, making them unsuitable for durable filaments.