Re: [Phys-L] superposition and interference

[John Denker <jsd@av8n.com>]

On 06/02/2014 10:42 AM, Bill Nettles wrote:
> When discussing waves in introductory university physics is there an
> important distinction to be made between the terms "superposition"
> and "interference?"

Wow, that's a challenging question.

This appears to be one of those tricky situations where 
there is a distinction, but it is rather technical and 
not necessarily relevant to the introductory course.

Ask yourself:  Is there any situation where we could
have superposition without interference?

The answer depends on how closely you look.  In some
practical sense, the superposition of two flashlight
beams results in no perceptible interference, because
the sources are incoherent.

The one-sentence explanation is that when you superpose
two waves, there is always interference if you look
closely enough, but there are lots of practical situations
where the interference is so washed out that you can't
see it.

==============

Incoherence is related to coherence in much the same
way as classical mechanics is related to quantum 
mechanics.  It is related to the often-observed but
seldom-understood fact that a cloud can change shape
and/or disappear into thin air.

This /can/ be explained in detail at the first-year 
college level, or even at the grade-school level:
  http://www.av8n.com/physics/wave-add.htm