Saturday, 13 September 2014

Wave reflection and open end boundary condition intuition


I need to understand one seemingly simple thing in wave mechanics, so any help is much appreciated!


When a pulse on a string travels to the right toward an open end(like a massless ring that is free to oscillate only in the vertical direction), then when the wave reaches the end it gets reflected and it becomes a positive pulse traveling to the left. So, my first question is, why do we even have reflection in this case(as far as energy and forces go)? What causes it in physical terms(intuitively)? And why for an open end the reflected wave is a positive wave and why for a closed end the reflected wave is a negative wave? An explanation using the tension of the string and energies will be much appreciated.


Also, for the open end case, the massless ring will have an amplitude of two time the amplitude of the incident wave while the wave gets reflected. Why is this the case? (or to state it differently why does the ratio of the amplitude of the transmitted wave divided by the amplitude of the incident wave equal to +2?).


Thank you!


ΝΟΤΕ: I want an explanation using forces or energy and not "image waves"




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