Question

Most people had never heard of a sound channel. Give two examples of cancellation for sound, light, water, and earthquakes. Explain why cancellation is so difficult to observe for light.

Answer 1

Cancellation of sound is observed where two loudspeakers are playing the same sounds. For the audience, there are few positions where the minimum of sound intensity occurs and so these are the locations where cancellation occurs.

For light, this is seen in a diffraction pattern when a Laser light is made to pass through a pinhole.

For water, waves emanating from a narrow window produces similar interference pattern thereby showing cancellation and similarly for earthquakes where few regions are affected the least due to their geographic locations coinciding with the minima positions.

Cancellation is difficult to observe with light because its wavelength is very small. Many orders smaller than the wavelengths of the above waves. This means that the obstacle must be very small to produce the cancellation (interference pattern) and the phase difference between the adjacent waves must be maintained for several time periods of the wave.