We assume that the wave front
passes at the position x=0
at the instant t=0.
So, at the instant t
the wave front has traveled a distance vt.
We want to know the displacement
at the position x
at the instant t.
For that we need to know how many cycles
are executed by the oscillatory movement
at the position x
at the instant t.
This is equal to the number of wave lengths
in the part of the wave that already past
the position x.
Hence,
number of cycles = (vt-x)/λ
For example in the above figure
(vt-x)/λ = 4.1.
|
|
