Walter Lewin's riddle

by Nikitin
Tags: lewin, riddle, walter
Nikitin is offline
Feb16-13, 07:07 AM
P: 588

At 37:00 he charges a conductor with a dielectric inside, removes the conductor plates and discharges them, and in the end puts them back into position.

Then something "remarkable" happens - when he connects the conductor plates with each-other, a spark is produced. Why did this happen?


Is this because the dielectric is still polarized when he puts back the plates, and thus the plates themselves become charged (by induction) in turn? If not, what is the answer to this riddle?
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jfgobin is offline
Feb16-13, 07:54 AM
P: 90
You're on the right track. If you want to put some math on it, consider the simpler case of a plane capacitor, with a dielectric and two gaps. Calculate the field both in the gaps and in the dielectric needed to have a potential difference around 20kV between the two plates, and compare to the breakdown field for air (around 3MV/m)
DrZoidberg is offline
Feb16-13, 08:02 PM
P: 371
Walter Lewin explains how this works here

atyy is offline
Feb16-13, 08:38 PM
Sci Advisor
P: 8,005

Walter Lewin's riddle

How did he discover this?
vanhees71 is offline
Feb17-13, 03:58 AM
Sci Advisor
P: 2,132
This is marvelous! I could listen to this guy the whole day :-)).

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