Superposition of Waves
Discuss the following with your class -
What do you think will happen when two waves in a medium meet? Will they kill each other? Or bounce upon each other? How will they interact?
Draw the diagrams above to explain the phenomenon. These are two square waves moving towards each other. Tell them that this is what happens when the waves meet. Ask them to explain what could have happened.
When these two meet, the waves add up to give the resultant wave over the region of overlap. This is called the principle of superposition, which can be stated as (stress upon the bolded words):
When two waves overlap, the resulting displacement of the medium at any location is the algebraic sum of the displacements of the individual waves at that same location.
The overlapping of waves is called interference of waves and the waves are said to be interfering with each other.
Now ask this question to the class - what will happen if two pulses of equal amplitude and wavelength, but inverted with respect to each other, meet? You may draw a diagram on the board to make things clearer. The result will be no displacement at all at the points where the two waves exactly overlap.