Consider a plane wave with peak pressure amplitude
propagating
from wave impedance
into a new wave impedance
, as shown in
Fig.C.15. (Assume
and
are real and positive.)
The physical constraints on the wave are that
As derived in §C.7.3, we also have the Ohm's law relations:
These equations determine what happens at the junction.
To obey the physical constraints at the impedance discontinuity, the
incident plane-wave must split into a reflected plane wave
and a transmitted plane-wave
such that
pressure is continuous and signal power is conserved. The physical
pressure on the left of the junction is
, and the
physical pressure on the right of the junction is
, since
according to our set-up.