From: Paul Doherty (pauld@exploratorium.edu)
Date: Mon Apr 30 2001 - 12:31:18 PDT
Message-Id: <l0311070bb7136c722153@[192.174.2.173]> Date: Mon, 30 Apr 2001 12:31:18 -0700 From: Paul Doherty <pauld@exploratorium.edu> Subject: Re: pinhole Liquid Nitrogen Questions (to Paul D.)
>Hi Paul,
>
>Here are those liquid nitrogen questions I was talking
>to you about earlier that my eighth graders asked me
>after seeing a demonstration on liquid nitrogen. I
>didn't see the demonstration myself, as I was
>observing other workshops with the other grades at the
>time):
>
>1. What is the chemical formula of liquid nitrogen?
N2
>
>2. Where can you get it from and how do you safely
>keep it?
You get it from welding supply stores and you keep it in special containers
called Dewars. Which are insulated bottles to keep it from boiling.
>
>3. What happens to the molecules as it forms?
The high speed gas molecules slow down and stick together to form a liquid.
>
>4. Can you touch an object after it is dipped in
>liquid nitrogen?
You can only touch it briefly. Touch it for more than a second and it can
freeze your flesh, killing your flesh locally and giving you frostbite.
Use tongs or gloves to hold things that have been in liquid nitrigen.
>
>5. Why did a light bulb get brighter after (the
>wires/socket?) were dipped in liquid nitrogen?
The resistance to electric current flow through a wire goes down when the
wire gets cold. The atoms of the wire bounce around when they are hot and
get in the way of electrons in the current. Cool the wire, the atoms bounce
around less and the electrons move through the wire with fewer collisions.
>
>6. At what temperature does liquid nitrogen freeze? It freezes at about
>-210 degrees celcius.
>
>7. How is it used in medical science, or other
>branches of science?
Doctors spray it on flesh to give you a spot of frostbite to remove spots
that might turn in to cancers, and to remove small moles.
If you cool wires enough they become superconductors with no resistance at all.
>
>Thanks Paul. Again, I didn't see the demonstration,
>but they got some good questions out of it.
>
>Dave.
>
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Paul "But it is more complicated than that!" Doherty,
Senior Staff Scientist, The Exploratorium.
pauld@exploratorium.edu, www.exo.net/~pauld
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