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1- destructive interference- when two waves interfere together , the have the same amplitude in the opposite direction . When two waves meet in the following example , they collide and go apart as crests and troughs . When the two amplitudes have opposite signs , they will also form a wave of lower amplitude. The following video shows two pulses interfering destructively . Again , they move away from the point where they combine as if they never met . As the crest and trough meet they cancel out .

 

2-constructive interference –  constuctive interference occurs when a crest from one source meets a crest from another source , the energies combine to displace the medium.  As the waves meet , the amplitude between the wave and crest becomes much larger . For two waves of equal amplitude interfering together, the resulting amplitude is twice as large as the orginal . Due to the constructive interference we were able to find a significant increase in amplitude.

 

 

How do noise – cancelling headphones use wave interference to eliminate unwanted sound  –

noise cancelling headphones are specifically desgined to emit their own sound waves cancelling those waves coming from the environment which results in silence