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Chapters 22/23 |
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Waves / Sound |
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Wave motion is the means of transferring energy
through a medium without the material itself moving along with the energy. |
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Mechanical Waves require a physical disturbance
in an elastic medium. |
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Sound |
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Electromagnetic waves involve electric and
magnetic disturbances and do not require any medium. |
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Light, radio waves, heat |
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Transverse waves transfer energy in such manner
to cause the material to vibrate perpendicular to the direction of wave
motion. |
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Longitudinal waves transfer energy in such a
manner to cause the material to vibrate parallel to the direction of wave
motion. |
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The speed (v) of sound through a material
depends on the elasticity and the density of the material. |
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More elastic é restoring forces é speed |
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More dense ê resistance to motion é speed |
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Wavelength (l) is the distance between two
adjacent particles that are in phase. |
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Frequency ( f ) is the number of waves (or
cycles) per unit of time. It is commonly measured in hertz (1 Hz = 1 cycle
/second). |
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Period ( T )is the the time per cycle, the
reciprocal of the frequency. |
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Superposition principle states that when two or
more waves exist simultaneously in the same medium,the result is the
algebraic sum of each wave. |
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Constructive interference produces a resulting
wave of greater amplitude. |
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Destructive interference produces a wave of
lesser amplitude. |
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Physical property |
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intensity |
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frequency |
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waveform |
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Perception |
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loudness |
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pitch |
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quality |
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Intensity is the measure of power per unit of
area. For a point source, the effective area would be a sphere with a
radius equal to the distance from the source. |
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Intensity levels compare the level of sound to
the hearing threshold. The ratio is described in decibels. |
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Infrasonic |
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frequencies less than 20 Hz |
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Audible sound |
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frequencies between 20 Hz and 20,000 Hz |
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Ultrasonic |
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frequencies greater than 20,000 Hz |
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A change in the observed frequency as a source
of sound moves relative to the observer. |
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Notes