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Re: A MC question on EM Induction

Hi;

You can make a very nice lab exercise out of this (this was in Physics
Teacher or Am J Phys a number of years ago) which establish's Faraday's
law.

Use a LabPro (from Vernier) or almost any A/D device which will capture
the voltage pulse. (You need around, say 200, points in a .5s interval).
You will see a postive voltage peak as the magnet goes into the coil and
a negative peak as it come off. The width of the peaks and the length of
the magnet can determine the magnet speed.

For different numbers of turns in the coil have students plot the peak
to peak voltage vs number of coils. (EMF proportional to N)

For different heights with one coil have students plot speed versus peak
voltage. (EMF proportional to delta B/delta t)

Ask them to explain what happens when you turn the magnet over, why the
lagging peak is just a bit higher than the first peak.

We do this in our sophomore labs. Two caveats:
1) Don't get the magnet near the calculator or LabPro (or credit cards
etc.)
2) Don't let the magnet hit the floor, it can change the magnetism (we
use rubber pads).



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Subject: Re: A MC question on EM Induction
Date: Tue, 23 Apr 2002 10:29:25 -0500
From: Mark Larchez <LarchezM@UWSTOUT.EDU>

At 10:55 AM 2002-04-19 -0500, you wrote:
doing demostration that involves
dropping a magnet through a PVC pipe. An emf is induced in a coil of
wire around the pipe and LED's light up.


This sounds like a neat demo. I'd like to try it. Could I have some hints
about the details, please?

Should I wind the wire around a long section of the pipe and look for
steady light?

Should I wind many turns around a small section near the bottom of the pipe
and watch for a flash of light?

---------------------------------------------------------------------
Mark Larchez larchezm@uwstout.edu
Physics Dept. voice or message (715) 232-2153
University of Wisconsin-Stout Dept. Office (715) 232-2626
Menomonie WI 54751 USA fax (715) 232-1437
---------------------------------------------------------------------

------------------------------------------------------------------------

Subject: Re: A MC question on EM Induction
Date: Tue, 23 Apr 2002 11:48:16 -0500
From: "Fakhruddin, Hasanbhai" <hfakhrud@BSU.EDU>

I have a spool of a large number of turns of wire (may be 500 turns) The free ends of the coil are connected to 2 LED's in parallel but oriented in opposite directions. The two LED's would preferably be of two different colors. The pvc pipe is held vertical and the spool is held around the pipe somewhere in the lower third of the 6-ft long pipe. The magnet should be of a strong variety.

AS the magnet falls through the pvc pipe and crosses the coil you will see very brief successive flashes of light from the two LED's. Hope this helps.

-Hasan Fakhruddin

-----Original Message-----
From: Mark Larchez [mailto:LarchezM@UWSTOUT.EDU]
Sent: Tuesday, April 23, 2002 11:29 AM
To: PHYS-L@lists.nau.edu
Subject: Re: A MC question on EM Induction

At 10:55 AM 2002-04-19 -0500, you wrote:
doing demostration that involves
dropping a magnet through a PVC pipe. An emf is induced in a coil of
wire around the pipe and LED's light up.


This sounds like a neat demo. I'd like to try it. Could I have some hints
about the details, please?

Should I wind the wire around a long section of the pipe and look for
steady light?

Should I wind many turns around a small section near the bottom of the pipe
and watch for a flash of light?

---------------------------------------------------------------------
Mark Larchez larchezm@uwstout.edu
Physics Dept. voice or message (715) 232-2153
University of Wisconsin-Stout Dept. Office (715) 232-2626
Menomonie WI 54751 USA fax (715) 232-1437
---------------------------------------------------------------------

------------------------------------------------------------------------

Subject: Re: A MC question on EM Induction
Date: Tue, 23 Apr 2002 12:58:19 -0400
From: hERBERT H GOTTLIEB <herbgottlieb@JUNO.COM>

Mark's idea of dropping a magnet through a solenoid (below) sounds like a
really
"neat" demo. Several years ago, in my advanced placement physics
course, a student was interested in predicting the waveform that would
be produced
on an oscilloscope when a bar magnet at rest was permitted to free-fall
through a vertical solenoid 50 cm long.

The class made their predictions and the trace on the oscilloscope screen
was photographed to see whose prediction was closest to the actual
photograph. It really sparked interest with the joy of true discovery
for the class.

Herb Gottlieb from New York City
(Where low salaries in the high schools are driving out our best physics
teachers now.)

********************************************************************

On Tue, 23 Apr 2002 10:29:25 -0500 Mark Larchez <LarchezM@UWSTOUT.EDU>
writes:
At 10:55 AM 2002-04-19 -0500, you wrote:
doing demostration that involves
dropping a magnet through a PVC pipe. An emf is induced in a coil
of wire around the pipe and LED's light up.

This sounds like a neat demo. I'd like to try it. Could I have some
hints about the details, please? Should I wind the wire around a long
section of the pipe and look for steady light?
***************************************
YES! It's certainly worth trying
******************************************
Should I wind many turns around a small section near the bottom of the
pipe and watch for a flash of light?
*****************************************
YES! It's certainly worth trying.
****************************************


--
------------------------------------------
"There are twice as many people in the
world as when I was born."
kf

kyle forinash 812-941-2390
kforinas@ius.edu
http://Physics.ius.edu/
-----------------------------------------