Let us assume that in the same propagation medium, two (harmonic) waves of the same frequency are superposed: | ||

For simplicity, let us assume that they are also equal in amplitude: |
||

Let us call When we say that the sources are emitting rhythmically, it means, for
example, that at the instant Then, taking |
||

By applying the preceding Superposition Principle together with standard trigonometric formulae (sum of trigonometric ratios), we obtain the following equation for the interference of waves of equal frequency and amplitude: | ||

The first term (between square brackets) does not depend on time, but
only on the position of the point considered in the propagation medium.
Therefore, this is the equation of a wave of variable amplitude |
||

Problems: P10607. |