Re: Wave phase reversal on reflection

[brian whatcott <inet@INTELLISYS.NET>]

At 09:43 4/24/00 -0600, you wrote:
> My colleague asked if there were a good explanatiion for the phase
> reversal when a wave reflects from a boundary where the new speed will be
> less and not when going from slow to fast. I don't have one for her. Can
> anyone help?
>
> Ken Fox
> AP/IB Physics Teacher
> Smoky Hill High School, CO

A plausible physical example which is somewhat relevant is provided by
a narrow pulse launched into a length of coax cable shorted at the far end.

 The terminal short is not a good match to the coax characteristic
impedance of 50 to 100 ohms, so the pulse energy is not absorbed at
the short.

On the other hand, it is evident that the electric field, potential,
PD or EMF at the short (take your pick of which is "correct") is constrained
 to be close to zero - so that a pulse travelling one way, can be considered
to be cancelled at the short by the inverted pulse reflected back at the
short.

 This example is extended to a continuous sine wave which is contrained to
the nodal (null) value at the terminal short, and which provides
nodes at intervals along the return path.



brian whatcott <inet@intellisys.net>
Altus OK