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Siemens Stiftung

The Ear, Hearing and Hearing Impairment: Sound absorption

Graphic:
If sound waves strike an obstacle with a corresponding material structure, they are absorbed, i.e. the entire mechanical energy of the sound is converted into thermal energy.

This effect is enhanced by sound barrier walls made of porous materials. By means of multireflection and dispersion, the passage of sound in such materials is extended considerably. The sound peters out.

Information and ideas:
Reference to students' everyday world: silence after snowfall.
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 Ear, Hearing and Hearing Impairment;: Sound reflection - experiments

Experimentation instructions:
Experiment on sound reflection.

Without the metal plate, the ticking would be barely audible, but in the appropriate position, it can be heard very clearly: Sound waves are partly reflected when they hit an obstacle. The angle of incidence is just as big as the angle of reflection.

Information and ideas:
The experiment can be done in class together with the students.

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

Medientypen

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Lernalter

11-18

Schlüsselwörter

Sound Wave (physics)

Sprachen

Englisch

Dieses Material ist Teil einer Sammlung

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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

Ultrasound materials testing - principle

Labeled graphic:
From the delay differences of the echoes recorded, layer thicknesses, errors and consistency can be calculated with oscilloscope graphs.

In engineering the checking of the quality of materials is an important task. A cheap way of testing materials where the material to be tested is not destroyed is based on the reflection of sound on interfaces.

Information and ideas:
These tasks are good for showing how behaviour of sound is used in practice.
Furthermore, internet research is good for explorative learning.

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

Medientypen

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Lernalter

11-18

Schlüsselwörter

Electroacoustics Sound Wave (physics)

Sprachen

Englisch

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Siemens Stiftung

Sound reflection

Graphic:
When sound waves hit an obstacle, they can be reflected in a similar way to light.

When a sound wave hits a large, hard surface, sound reflection occurs:
Sound is reflected by the surface just as light is reflected by a mirror.

Information and ideas:
Reference to students' everyday world: Echo in the mountains.
Can be checked with the students in an experiment.

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

Medientypen

Bild

Lernalter

11-18

Schlüsselwörter

Sound Wave (physics)

Sprachen

Englisch

Bild

Siemens Stiftung

Sound diffraction

Graphic:
Diffraction is a typical feature of sound waves when they meet an obstacle.

The diffraction of sound waves is a physical mechanism which ensures the entry of sound waves into acoustic shadows.
That means the sound is audible in areas which are cut off from the direct sound incidence, such as behind obstacles.

Information and ideas:
Diffraction of light can be proved when a parallel ray beam of monochrome light is directed at a narrow opening. A screen set up behind the opening gives us a diffraction figure (bright and dark stripes that lose intensity the further outwards they are). With sound, a direct reference to the students' everyday world is even easier: Why can you hear noise from a street in front of a building even when you are behind the building?
Further information about this graphic is provided as an information sheet on the media portal of the Siemens Stiftung.

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

Medientypen

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Lernalter

13-18

Schlüsselwörter

Chart Optics Sound Wave (physics)

Sprachen

Englisch

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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

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Siemens Stiftung

;: Color and voltage of LEDs

Photo:
The operating voltage of LEDs depends on the color. This is an indication of discrete energy levels and the photon character of light.


What color an LED emits depends on the energy level of the charge transition from the non-conduction band to the conduction band. Depending on the basic material (Si, GaAs, GaN etc.) and doping, as well as the internal resistance every LED has a typical operating voltage (voltage = potential = energy difference). Although this is modified by the design (internal resistance, etc.), in the final analysis it is determined by the discrete energy level of the charge transition between non-conduction and conduction band.

Information and ideas:
The abstract principle of the quantization of energy in the form of photons is demonstrated clearly in an extremely simple experiment with four LEDs and a power supply unit. Red LEDs light up at a voltage from about 1.5 volts, yellow from about 1.9 volts, green from about 2.3 volts and blue from about 3.3 volts.
Instructions for building a variable LED color mixer can be found in the experimentation instructions "Experiments - energy quantization with LEDs" on the media portal of the Siemens Stiftung.

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Siemens Stiftung

Sound refraction

Schematic diagram:
Sound refraction in air with different temperature layers (from warm to cold).

The speed of sound in the air depends on the density and thus the temperature of the air: At high temperatures, the sound travels faster than it does at lower ones. So when sound moves from a warm layer of air to a colder one, its speed decreases.
However, the direction in which the sound spreads also changes as the speed changes. It is said that the sound wave is "broken?. In the case described, i.e. when sound moves from a warm to a cold layer of air, the sound wave is broken upwards.

Information and ideas:
How does sound behave when it moves from a colder to a warmer layer?
Is it correct that you hear worse against the wind than with the wind?
The latter can be checked together with students in an experiment.
A comparison with the refraction of light rays can be made.

Relevant for teaching:
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