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Siemens Stiftung

How does a shark hear?

Graphic:
Shark and its hearing organ (lateral-line organ).

The shark as an example of an animal that mainly hears with its body surface. The sense of hearing (lateral-line organ) is sketched in.
Information and ideas:
Picture to introduce topic "How do animals communicate with each other?".
Further information regarding this graphic is available as information sheet on the media portal of the Siemens Stiftung

Relevant for teaching:
Sound/acoustics: hearing range, hearing frequency limit
Communication, Understanding

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Siemens Stiftung

The Ear, Hearing and Hearing Impairment: Acoustic scattering

Graphic:
Acoustic scattering. One of several ways sound waves react when they hit an obstacle.

Scattering is a reflection of small structures in no particular preferred direction. It is very much dependent on frequency.

Information and ideas:
Can be checked with the students in an experiment.

Relevant for teaching:
Sound/acoustics: parameters
Vibrations and waves

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Siemens Stiftung

The singing wine glass

Photo:
Rubbing a wine glass can produce tones.

If you rub along the rim of a wineglass with a wet finger this produces a tone. As soon as the glass produces a tone, short-wave marginal waves appear in the liquid. The glass oscillates back and forth at those places at which the waves occur. Between them it is still. The oscillation of the glass is not only transferred to the liquid but also to the air and in this way reaches our ear in the form of a fine tone.

Information and ideas:
This experiment can be done easily in class - the class might even make a glass harmonica on their own?
Further information on this photo is available as information sheet on the media portal of the Siemens Stiftung.

Relevant for teaching:
Acoustic phenomena
Sound/acoustics: parameters
Vibrations and waves

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Siemens Stiftung

The Ear, Hearing and Hearing Impairment: Refraction

Graphic:
The wave front model of refraction on an interface makes it clear why the direction of the sound propagation changes.

When waves cross over from one medium to another, the speed at which the waves spread changes. Consequently, the wave normals of the incident and broken waves have different directions. With light waves, the change in the index of refraction at the boundary is the cause; with sound waves, it is the change in the density.
The graphic illustrates the case when the speed of propagation becomes slower at the transition from the first to the second medium: The wave is broken at the perpendicular of the boundary surface.
An explanation of this phenomenon is provided by the Huygens' Principle: Every point on a wave front is the starting point for a new wave, known as an "elementary wave". The enclosing end of the elementary wave creates the new wave front.

Information and ideas:
Refraction at boundaries also occurs with sound waves (for example, in the atmosphere at the transition from warm to cold layers of air).

Relevant for teaching:
Sound/acoustics: parameters
Vibrations and waves

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Siemens Stiftung

The Ear, Hearing and Hearing Impairment: Diffraction

Graphic:
Diffraction of waves on encountering an obstacle.

The graphic shows possible diffraction effects according to aperture and wave length.

Information and ideas:
Diffraction arises in sound waves as well, for example at corners of buildings.
Further information regarding this graphic is available as information sheet on the media portal of the Siemens Stiftung.

Relevant for teaching:
Sound/acoustics: parameters
Vibrations and waves