Which metal is used for filaments in light bulbs?

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

Answer: (A)

The thing being tested is why a filament lasts long enough to emit visible light despite being heated to extreme temps. Tungsten is ideal because it has an exceptionally high melting point and remains strong at high temperatures. This lets a very thin tungsten wire glow brightly without melting. It also has a low vapor pressure when hot, so atoms don’t evaporate away quickly, which keeps the filament from thinning and breaking over time. In an incandescent bulb, the filament needs to reach thousands of degrees to emit visible light, and tungsten can do that while staying intact in the bulb’s vacuum or inert environment.

Other metals would fail under these conditions: copper and aluminum melt at much lower temperatures, so they would burn through or deform; nickel doesn’t withstand evaporation and creep as well, leading to a much shorter bulb life.