Re: Light bulbs

[Leigh Palmer <palmer@SFU.CA>]

At 15:21 -0700 8/22/99, David_Anderson wrote:
> Aren't we getting a little distracted whether light bulbs have a good
> vacuum or not?  That really isn't the point.  The point is does glass flow
> or not.

Note the subject: Light bulbs. Glass doesn't flow. That's a non-topic.

Light bulbs are very interesting, and I like to point that out to my
elementary school students. There is a nice experiment you can do in
your kitchen with a burnt-out (though that is not a requirement)
bulb. Crush the base of the base gently under water in the sink with
a pair of channel locks around the very bottom of the threads. The
bulb should be held base down. You will fracture the pumpout, and
some water will be sucked* into the bulb because the nitrogen inside
is at a pressure somewhat less than an atmosphere. Some among you
may be surprised to learn how much gas there is inside.

Look at an old light bulb, preferably one with a clear envelope. You
should see some part of the envelope darkened with long use. What is
the material on the inside of the bulb? How do you suppose it got
there? (Antigravity is not one of your choices.) Imagine what the
500 watt bulb inside a Zeiss Planetarium Projector must look like by
the time it is replaced.

Don't throw that wet light bulb away; carefully break it and remove
the filament. Examine it carefully with a magnifier. What do you see?
Do you suppose tungsten is a terribly ductile metal?

Leigh