pulse shape, was Graphing by hand

[LUDWIK KOWALSKI <kowalskil@alpha.montclair.edu>]

On 29 Sep 1997 Herb Gottlieb asked us to sketch V(t) generated in solenoid 
when a bar magnet is falling through it. 

For a bar magnet which is much longer than the solenoid I would expect four 
bell-shaped pulses: positive, negative, positive, negative. The maxima
would be progressively larger and larger, unless there is no acceleration. 
(The words "positive and negative" are used in the relative sense, "one 
with respect to another".)

For a bar magnet which is much shorter than the solenoid (as specified by
Herb) I would expect two bell-shaped pulses: positive and negative. The 
magnitudes of these would be smaller than for the very long magnet. One
pulse is generated when the magnet enters the coil and one whan it comes
out. Only a negligible V is induced when a short magnet is near the center 
of a long solenoid. 
                                                      Ludwik Kowalski
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> A small bar magnet, north pole down, is held 0.5 meter above the center 
> of  a vertical  air core solenoid. The solonoid is  0.5 meter long and 
> sufficiently wide to allow the bar magnet to fall through without 
> touching its coils.  A  voltmeter (or an oscilloscope) is attached to 
> the ends of the solenoid coils.
>
> Sketch a voltage vs time graph from the time that the magnet is released, 
> falls freely through the solenoid and emerges 0.5 meter below the 
> solenoid bottom.
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