Illustration for article titled Why a Broken Light Bulb Stays Lit If You Dip It In Liquid Nitrogen

Most of us think of liquid nitrogen as an extinguishing force, but it can, at times, rage against the dying of the light . . . bulb. Find out why a smashed light bulb stays lit if it's dipped in liquid nitrogen.


Smash a light bulb and it goes out — that much we learned from the latest alien invasion movie, The Darkest Hour. The heroes run around using light bulbs as indicators of when the aliens are around. When they light up people need to be on the look out. But if the bulbs are smashed, they're useless.

Not quite. If you happen to have a bucket of liquid nitrogen around, you can stick the bare filament in it, and it will turn on just fine. A light bulb works by running electrons through a filament fast enough and in great enough quantities that the resistance causes the filament to heat up so much that it glows brightly. That bright glow is only sustained because the inside of the bulb is either a vacuum or filled with an inert gas. If the bulb is cracked, it would fill with air, which contains a vital little thing we call oxygen. A sufficiently hot enough substance will cause its particles to team up with oxygen and flake away. This is known as 'oxidization,' or if you're not inclined to be fancy, 'burning.'

The process requires heat, and it requires oxygen. This is where the liquid nitrogen comes in. Although it seems like the light bulb would be extinguished by the cold of the liquid nitrogen — if it can't heat it can't glow — the electricity is still pumping through and heating the filament. Once the temperature gets high enough, the filament vaporizes the liquid around it. Vapor is a pretty good insulator, and so the nitrogen remains cold while the filament gets hot, with the vapor between maintaining the temperature difference.

The bulb glows continuously, flicking on and off when the switch is flipped, because the liquid nitrogen serves the same purpose as a vacuum or an inert gas. It keeps out the oxygen, making oxidization impossible. The filament can keep heating and heating, long past the temperature when it would usually flame out, because it lacks the materials to oxidize. If the bulb is taken out of the nitrogen and turned on, it will flare out instantly.


Top Image: Stef
Via Naked Scientists and Cryonics with Liquid Nitrogen.

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