This equation describes the standing waves on the string, where each value of
n corresponds to a different standing wave pattern. The standing wave patterns
are alternatively called the modes of vibration of the string. As we will see in
Section 6.4 these are the normal modes of the vibrating string.
The functions fn(x) = An sin (nπx/L) for n = 1 to 4 are plotted in Figure
6.2(a)–(d), respectively. For the purpose of these figures the amplitudes of the
four standing waves have been taken to be the same. For n = 1 we have
f1(x) = A1 sin
π
L
x
,
which gives the amplitude variation shown in Figure 6.2(a). This is the fundamental
mode or first harmonic of the string; n = 2 corresponds to the second harmonic,
n = 3 corresponds to the third harmonic, etc. We see that the number of antinodes
in the nth harmonic is equal to n. The corresponding angular frequencies ωn of
the standing waves are given by Equation (6.8) and are πv/L, 2πv/L, 3πv/L and
4πv/L, respectively. The time period T for a standing wave pattern to exactly to
reproduce its shape is given by