Illustration of solution We chose for our first illustration the situation when only a forward wave is present. The
wave may be illustrated against a time axis as shown in Figure 2.4. Because the function
Vf is of the single argument z − ct, if the voltage observed at the origin of position as a
function of time is represented by the solid curve in Figure 2.4, then at some position to
the right of the origin the same voltage as a function of time will be observed but at a later
time, as is shown by the dotted curve. As the observation point is moved progressively
to the right to larger values of the position coordinate z, there will be an increase in the
delay before the above defined voltage waveform is observed. All of these features are
illustrated in Figure 2.4.
The situation on the line may alternatively be represented as shown in Figure 2.5,
wherein at one particular time the voltage waveform for all points on the line is shown.
This illustration is for a wave of the same shape as was illustrated in Figure 2.4. If one
pictures the wave at later and later times, it will be seen to have moved further and
further to the right.
It is interesting to note the shape of the wave in this latter diagram appears to be a
mirror image of the one when drawn against the time axis. This is a natural consequence
of the fact that the shape of the forward wave is an expressed as a function Vf of the
single argument z − ct and the coefficients of z and t in that combination have different
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