1. Wave Superposition

2. The principle of superposition
Whenever two waves are travelling in the same region the total displacement at any point is equal to the vector sum of their individual displacements at that point

3. Here two waves are in phase and occupy the same space
Here two waves are in phase and occupy the same space. To find the resultant wave just add the heights of the waves together

4. Here adding the heights of the waves together results in no wave as the waves are out of phase by π

5. Two waves approach each other and cross
Two waves approach each other and cross. At each point the height of the combined wave is the sum of the heights of the individual waves

6. Here two waves have the same wavelegths but different frequencies
Here two waves have the same wavelegths but different frequencies. Observe what happens as they pass from phase to antiphase

7. Here a wave and its reflection are in the same region of space
Here a wave and its reflection are in the same region of space. The reflected wave from the right has the same wavelength and frequency as the incident wave.
Notice how stationary points called nodes occur. Exactly in between the nodes we have the point of greatest displacement called antinodes.
What is observed is a STATIONARY WAVE.

8. Stationary Waves
A stationary (standing) wave results when two waves which are in opposite direction,s and which have the same speed and frequency and approximately equal amplitudes are superposed

9. Wave superposition
Interactive Java Applet

10. Notice that one wavelength is the distance between 3 nodes or antinodes