Echoes occur when a reflected sound wave reaches the ear more than 0. If the elapsed time between the arrivals of the two sound waves is more than 0. In this case, the arrival of the second sound wave will be perceived as a second sound rather than the prolonging of the first sound.
There will be an echo instead of a reverberation. Reflection of sound waves off of surfaces is also affected by the shape of the surface. As mentioned of water waves in Unit 10 , flat or plane surfaces reflect sound waves in such a way that the angle at which the wave approaches the surface equals the angle at which the wave leaves the surface.
This principle will be extended to the reflective behavior of light waves off of plane surfaces in great detail in Unit 13 of The Physics Classroom. Reflection of sound waves off of curved surfaces leads to a more interesting phenomenon. Curved surfaces with a parabolic shape have the habit of focusing sound waves to a point.
Sound waves reflecting off of parabolic surfaces concentrate all their energy to a single point in space; at that point, the sound is amplified. Perhaps you have seen a museum exhibit that utilizes a parabolic-shaped disk to collect a large amount of sound and focus it at a focal point. If you place your ear at the focal point, you can hear even the faintest whisper of a friend standing across the room.
Parabolic-shaped satellite disks use this same principle of reflection to gather large amounts of electromagnetic waves and focus it at a point where the receptor is located. Scientists have recently discovered some evidence that seems to reveal that a bull moose utilizes his antlers as a satellite disk to gather and focus sound. Finally, scientists have long believed that owls are equipped with spherical facial disks that can be maneuvered in order to gather and reflect sound towards their ears.
The reflective behavior of light waves off curved surfaces will be studies in great detail in Unit 13 of The Physics Classroom Tutorial. Diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path.
In that unit, we saw that water waves have the ability to travel around corners, around obstacles and through openings. The amount of diffraction the sharpness of the bending increases with increasing wavelength and decreases with decreasing wavelength.
In fact, when the wavelength of the wave is smaller than the obstacle or opening, no noticeable diffraction occurs. Diffraction of sound waves is commonly observed; we notice sound diffracting around corners or through door openings, allowing us to hear others who are speaking to us from adjacent rooms. Many forest-dwelling birds take advantage of the diffractive ability of long-wavelength sound waves.
Owls for instance are able to communicate across long distances due to the fact that their long-wavelength hoots are able to diffract around forest trees and carry farther than the short-wavelength tweets of songbirds. Low-pitched long wavelength sounds always carry further than high-pitched short wavelength sounds.
Scientists have recently learned that elephants emit infrasonic waves of very low frequency to communicate over long distances to each other.
Elephants typically migrate in large herds that may sometimes become separated from each other by distances of several miles. Researchers who have observed elephant migrations from the air and have been both impressed and puzzled by the ability of elephants at the beginning and the end of these herds to make extremely synchronized movements. The matriarch at the front of the herd might make a turn to the right, which is immediately followed by elephants at the end of the herd making the same turn to the right.
If the wavelength is much smaller than the obstacle opening , there will not be much, if any, diffraction. Since the wavelength of visible light is on the order of 0.
Sound waves, on the other hand, have a wavelength on the order of 1 meter and diffract very easily. This allows sound waves to bend around corners. Why can't light go around corners? And why can sound? Answer 1: The answer to this question has to do with the fact that both light and sound are made up of waves.
The amount of diffraction the sharpness of the bending increases with increasing wavelength and decreases with decreasing wavelength. In fact, when the wavelength of the wave is smaller than the obstacle or opening, no noticeable diffraction occurs.
Diffraction of sound waves is commonly observed; we notice sound diffracting around corners or through door openings, allowing us to hear others who are speaking to us from adjacent rooms. Many forest-dwelling birds take advantage of the diffractive ability of long-wavelength sound waves.
Owls for instance can communicate across long distances since their long-wavelength hoots are able to diffract around forest trees and carry farther than the short-wavelength tweets of songbirds. Low-pitched long wavelength sounds always carry further than high-pitched short wavelength sounds. Scientists have recently learned that elephants emit infrasonic waves of very low frequency to communicate over long distances to each other. Elephants typically migrate in large herds that may sometimes become separated from each other by distances of several miles.
Researchers who have observed elephant migrations from the air and have been both impressed and puzzled by the ability of elephants at the beginning and the end of these herds to make extremely synchronized movements.
The matriarch at the front of the herd might make a turn to the right, which is immediately followed by elephants at the end of the herd making the same turn to the right. These synchronized movements occur even though the elephants' vision of each other is blocked by dense vegetation. Only recently have they learned that the synchronized movements are preceded by infrasonic communication. While low wavelength sound waves are unable to diffract around the dense vegetation, the high wavelength sounds produced by the elephants have enough diffractive ability to communicate long distances.
Bats use high frequency low wavelength ultrasonic waves to enhance their ability to hunt. The typical prey of a bat is the moth - an object not much larger than a couple of centimeters. Bats use ultrasonic echolocation methods to detect the presence of bats in the air. But why ultrasound? The answer lies in the physics of diffraction. As the wavelength of a wave becomes smaller than the obstacle that it encounters, the wave is no longer able to diffract around the obstacle, instead the wave reflects off the obstacle.
Bats use ultrasonic waves with wavelengths smaller than the dimensions of their prey. These sound waves will encounter the prey, and instead of diffracting around the prey, will reflect off the prey and allow the bat to hunt by means of echolocation. Refraction of waves involves a change in the direction of waves as they pass from one space to another.
Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves. So, if the space or its properties are changed, the speed of the wave is changed.
Thus, waves passing from one space to another will undergo refraction. Refraction of sound waves is most evident in situations in which the sound wave passes through a space with gradually varying properties.
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