Re: Today's jaw dropper

[Leigh Palmer <palmer@sfu.ca>]

> At 19:25 10/5/97 -0700, you wrote:
>
> > I got one for you from Wilson's COLLEGE PHYSICS 3rd Ed, Q15.64.  The
> > problem states that an electron is moved tthrough a potention of 10^8 V
> > in a lightning discharge.  Ignoring collisions, what KE does it gain?
> > The supposed e- gains 10^8 eV of KE.
> >
> > Now, my reasoning is that an e- masses about 5x10^5 eV.  Guess how fast an
> > electron with a KE of 10^8 eV is going.
>
> 0.9c+  I imagine, if I ignore collisions - a vacuum like medium.
> Am I missing something?

The impression might be taken by a naive student that such electron
velocities actually occur in the lightning phenomenon. It is unclear
to me that mentioning lightning at all in this problem has any
justification whatever. It is an example of gratuitous sex - trying
to make the problem "more interesting" or, in ancient language,
"relevant". (That is the most common reason for including skin shots
in modern movies. They aren't essential to the story, but they put
bottoms into theater seats.) The author is misguided in doing so;
only misconception can result from this excess.

Leigh