Question

17. Noise-cancelling earphones use which of the following phenomena?

Answer 1

Noise cancelling earphones reduce the noise in two ways.

i) The material and the high density foam in some earphones act as sound absorber and reduces noise to some extent.

ii) Most importantly, effective noise cancelling earphones use the phenomenon of Interference of waves. Here the earphones produce the same frquency waves as that of the waves of the noise, with the same amplitude but with a phase difference of 180^o. So the interference is destructive, that is the intensity of the incoming noise is canselled out by the waves produced by the earphones.