Issues in calibration. Primary reference standards. A reference standard for a unit of measurement is an artifact that embodies the quantity of interest in a way that ties its value to the reference base. At the highest level, a primary reference standard is assigned a value by direct comparison with the reference base.
Refraction of Sound. Refraction is the bending of waves when they enter a medium where their speed is different. 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. But bending of sound waves does occur and is an interesting phenomena in sound.
When sound changes mediums (enters a different material) at an angle other that 90 degrees, it is bent from its original direction. This change in angle of direction is called refraction. Because of the angle, part of the wave enters the new medium first and changes speed.The difference in speeds causes the wave to bend. The velocity of sound in each material is determined by the material properties (elastic modulus and density) for that material.his change in angle of direction is called refraction. Because of the angle, part of the wave enters the new medium first and changes speed. The difference in speeds causes the wave to bend. The velocity of sound in each material is determined by the material properties (elastic modulus and density) for that material.