But the voice comes again, "Good morning". You are just about at the point of questioning your sanity anyway, being out at this time of the morning, so you decide to ignore it. Just as the sun rises over a cool lake, you may hear someone speak to you, saying "Good morning!". Consider that you have gone out to a lake before dawn. Natural amplifiers can occur over cool lakes.Įarly morning fishermen may be the persons most familiar with the refraction of sound. But refraction can add some additional sound, effectively amplifying the sound. Normally, only the direct sound is received. Normally, only that which is initially directed toward the listener can be heard, but refraction can bend sound downward. Sound propagates in all directions from a point source. Refraction of Sound If the air above the earth is warmer than that at the surface, sound will be bent back downward toward the surface by refraction. If you apply the right brake, the vehicle turns right because you have slowed down one side of the vehicle without slowing down the other. From the basic wave relationship, v=fλ, it is clear that a slower speed must shorten the wavelength since the frequency of the wave is determined by its source and does not change.Īnother visualization of refraction can come from the steering of various types of tractors, construction equipment, tanks and other tracked vehicle. When applied to waves, this implies that the direction of propagation of the wave is deflected toward the right and that the wavelength of the wave is decreased. Not only does the direction of march change, the separation of the marchers is decreased. The marchers on the left, perhaps oblivious to the plight of their companions, continue to march ahead full speed until they hit the slow medium. A column of troops approaching a medium where their speed is slower as shown will turn toward the right because the right side of the column hits the slow medium first and is therefore slowed down. These visualizations may help in understanding the nature of refraction. But bending of sound waves does occur and is an interesting phenomena in sound Refraction is not so important a phenomenon with sound as it is with light where it is responsible for image formation by lenses, the eye, cameras, etc. The aperture or the diffracting object effectively then becomes the second source of the wave.Refraction is the bending of waves when they enter a medium where their speed is different. The wave then bends around the corners of an obstacle, through apertures into the regions of the shadow of the obstacle. Note: Diffraction refers to the phenomenon of a wave encountering an opening or obstacle. Therefore to encounter diffraction on electromagnetic waves in our normal lives, we would require microwaves and not visible light since microwaves have a much higher wavelength and the longer wavelengths of about $3\ cm$ can be seen in low light conditions. This does not happen in electromagnetic waves.įor observing the phenomenon of diffraction, the order of the magnitude of the wavelength of the waves should be comparable to that of the slit width. The motion of vibration in longitudinal waves is in the same direction as the wave propagation. Sound travels by longitudinal waves which radiate outward in concentric circles. The general wavelength of visible light ranges from $7000 \times m$. The wavelength of sound generally ranges from $17\ m$ to $15\ mm$. The frequency of human audible sound waves lies from $20\ Hz$ to $20\ kHz$. The wavelength of sound waves is much higher than that of visible light. This condition is satisfied only for sound waves in everyday life. For diffraction to occur, the slit width should be comparable to the wavelength of the light or sound waves. Hint: The reason for the diffraction of sound waves being more evident in daily experience than light waves is that sound waves have much higher wavelength compared to the visible light waves.
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