The amplitude Ylll of a wave,, is the magnitude of the
maximum displacement of the elements from their equilibrium positions as the
wave passes through them. (The subscript m stands for maximum.) Because YIIl is
a magnitude, it is always a positive quantity, even if it is measured downward
instead of upward as drawn
The phase of the wave is the argument kx - wt of the sine . As the
wave sweeps through a string element at a particular position x, the phase
changes linearly with time t. This means that the sine also changes, oscillating
between + 1 and -1. Its extreme positive value ( + 1) corresponds to a peak of the
wave moving through the element; at that instant the value of Y at position x is Ym'
Its extreme negative value (-1) corresponds to a valley of the wave moving
through the element; at that instant the value of Y at position x is -Ym' Thus, the
sine function and the time-dependent phase of a wave correspond to the oscillation
of a string element, and the amplitude of the wave determines the extremes
of the element's displacement.

 

 

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