Re: [Phys-l] About light interference and energy preservation

["John Clement" <clement@hal-pc.org>]

> We were reading in class the book "Please Explain" by Isaac  Asimov,
> and answer 78 explains about light interference. It says that when
> two white light waves interfere destructively on a screen, we can
> obtain darkness in the screen, but energy should be converted to
> another form: heat (screen temperature raises up) . A student asked
> me about the case that white ligth interference were in perfect
> vacuum, ¿ in wich way can the energy conservation principle be
> preserved ? .¿ Energy will be manifested as heat ?. 

> That's easy.  Asimov's answer is fiction.  Not science
> fiction, just fiction.

Actually Asimov's attempted explanation is probably a common misconception.
I suspect that if you questioned students about interference and asked about
energy in the dark regions they might come up with a similar explanation.
Unfortunately accounts in books may not look at energy, and this is
particularly true in lower level books.  This is a huge mistake because
students have to develop conservation reasoning.

I suspect that many on this list may have misconceptions about chemical
topics, but Asimov would not.  It is unfortunate that this mistake is in one
of his books, and there is probably no way of changing it.  His writings on
science were generally quite good, but he admitted that his writings on
physics might have mistakes.  So his misconceptions was a reasoned
misconception, and not the usual more random misconceptions we encounter in
class.  So it actually has some scientific reasoning in it.  He just put the
energy in the wrong place.

John M. Clement
Houston, TX