Date: Wed Feb 14 12:44:12 2007

Author: Cliff Bettis

Subject: Re: Incandescent Bulb Destruction and Uses

Post:
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Assuming a light bulb in parallel with an electromagnet coil, powered by =
a power supply through a switch:

When you disconnect the power, the collapsing magnetic field tries to =
keep the current in the coil from changing. The only path for it to go =
through, is the hapless light bulb. The EMF developed across the bulb =
will be in the ratio of the filament resistance to coil resistance. For =
a 25 W bulb the operating temperature resistance is about 400 ohms. The =
coil resistance might be as little as a couple of dozen; so if you =
originally had 100 V across the coil light bulb parallel combination, =
when you open the switch removing the power supply, the EMF across the =
bulb could easily be thousands of volts (RIP bulb). By the way the =
current switches directions in the bulb when you open the switch.

I am surprised no one has mentioned 5D20.60 (Conduction in Glass) as a =
use for an old incandescent bulb.

Cliff
----- Original Message -----=20
From: William Maddox=20
To: tap-l@lists.ncsu.edu=20
Sent: Wednesday, February 14, 2007 9:41 AM
Subject: Re: [tap-l] Incandescent Bulb Destruction and Uses


From: WC Maddox

Save them for series and parallel circuit demos. Fluorescent bulbs =
work in parallel but there is a time delay before coming to full =
brightness. The ones I tried did not work in series. Instead got one =
bright, one dim, one no glow. Could be used but explanation more =
complicated. Need higher voltage power supply or lower voltage =
fluorescent bulbs for series circuit.

If you have a large horseshoe magnet and a setup like =
http://electro.physics.auburn.edu/~demo/em/5j/5j20_20.htm put the switch =
contacts between poles of the magnet. When you jerk open the switch you =
will get a bright flash. If you use 15 or 25 W bulbs the filament is =
sometimes burned out. If anyone knows what is happening, Dr. Williams at =
Auburn would like to know. He came up with this modification of time =
delay experiment. It is more than the discharge of the energy stored in =
coil and V=3D-Ldi/dt. The bulbs don't burn out if you don't use magnet.

End Message



At 08:35 AM 2/14/2007, you wrote:

I have two related questions. I have been replacing my incandescent =
bulbs with CFLs and not waiting until the bulbs burn out. As a result I =
have about a dozen various incandescent bulbs for which I have no good =
use. Rather then give them away or sell them, and have their energy use =
contribute to global warming...I was wondering if there are any good =
demonstrations or labs that safely destroy these bulbs that I could use =
over time.
=20
Secondly, is there a searchable archive of this list, and if so =
where is it kept?
=20
Sincerely,
Don B. Cameron
Physics / Chemistry / Earth / Fitness
University of Denver H.S.
2393 South York St.
Denver, CO 80208
dcameron@du.edu

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Assuming a light bulb in parallel with =
an=20
electromagnet coil, powered by a power supply through a =
switch:

When you disconnect the power, the =
collapsing=20
magnetic field tries to keep the current in the coil from changing. The =
only=20
path for it to go through, is the hapless light bulb. The EMF developed =
across=20
the bulb will be in the ratio of the filament resistance to coil =
resistance. For=20
a 25 W bulb the operating temperature resistance is about 400 ohms. The =
coil=20
resistance might be as little as a couple of dozen; so if you originally =
had 100=20
V across the coil light bulb parallel combination, when you open the =
switch=20
removing the power supply, the EMF across the bulb could easily be =
thousands of=20
volts (RIP bulb). By the way the current switches directions in the bulb =
when=20
you open the switch.

I am surprised no one has mentioned =
5D20.60=20
(Conduction in Glass) as a use for an old incandescent =
bulb.

Cliff

----- Original Message -----
From:=20
William Maddox
To: tap-l@lists.ncsu.edu
Sent: Wednesday, February 14, =
2007 9:41=20
AM
Subject: Re: [tap-l] =
Incandescent Bulb=20
Destruction and Uses
From: WC MaddoxSave them for series and =
parallel=20
circuit demos. Fluorescent bulbs work in parallel but there is a time =
delay=20
before coming to full brightness. The ones I tried did not work in =
series.=20
Instead got one bright, one dim, one no glow. Could be used but =
explanation=20
more complicated. Need higher voltage power supply or lower voltage=20
fluorescent bulbs for series circuit.If you have a large =
horseshoe=20
magnet and a setup like http://electro.physics.auburn.edu/~demo/em/5j/5j20_20.=
htm=20
put the switch contacts between poles of the magnet. When you jerk =
open the=20
switch you will get a bright flash. If you use 15 or 25 W bulbs the =
filament=20
is sometimes burned out. If anyone knows what is happening, Dr. =
Williams at=20
Auburn would like to know. He came up with this modification of time =
delay=20
experiment. It is more than the discharge of the energy stored in coil =
and=20
V=3D-Ldi/dt. The bulbs don't burn out if you don't use =
magnet.End=20
MessageAt 08:35 AM 2/14/2007, you wrote:
I have =
two related=20
questions. I have been replacing my incandescent bulbs with =
CFLs and=20
not waiting until the bulbs burn out. As a result I have about =
a dozen=20
various incandescent bulbs for which I have no good use. =
Rather then=20
give them away or sell them, and have their energy use contribute to =
global=20
warming...I was wondering if there are any good demonstrations or =
labs that=20
safely destroy these bulbs that I could use over=20
time. Secondly, is there a =
searchable=20
archive of this list, and if so where is it =
kept? Sincerely,Don B. CameronPhysics / Chemistry / Earth =
/=20
FitnessUniversity of Denver H.S.2393 South York =
St.Denver, CO=20
=
80208dcameron@du.edu

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