SOUND WAVES AND SPEED OF SOUND WAVES

SOUND WAVES

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ESCAPE ROOM

NATURE OF SOUND WAVES

• Created by a vibrating object such as the string on a violin, your vocal chords or the diaphragm of a loudspeaker.

• Sound waves can be transmitted through gases, liquids and solids.
• If there is no medium, there is no sound.

SOUND WAVE CHARACTERISTICS

• Condensation or Compression: Region of the wave where air pressure is slightly higher.

SOUND WAVE CHARACTERISTICS

• Rarefaction: Region of the air wave where the pressure is slightly lower.
• Pure Tone: A sound wave with a single frequency.
• Pitch: An objective property of sound associated with frequency. Pitch
• High frequency = high pitch.
• Low frequency = low pitch.
• Loudness: The attribute of sound that is associated with the amplitude of the wave.
• Beat: When two sound waves overlap with a slightly different frequency.

DOPPLER SHIFT

• The change in sound frequency due to the relative motion of either the source or the detector.

HIGH PITCH SOUND

LOW PITCH SOUND

STANDING WAVES IN MUSICAL INSTRUMENT

• Resonance: Stringed instruments, such as the guitar, piano or violin, and horn and wind instruments such as the trumpet, oboe, flute and clarinet all form standing waves when a note is being played.

STANDING WAVES IN MUSICAL INSTRUMENT

• The standing waves are of either the type that are found on a string, or in an air column (open or closed).
• These standing waves all occur at natural frequencies, also known as resonant frequencies, associated with the instrument.

WAVE INTERFERNCE

• Wave interference is the phenomenon, which occurs when two waves meet while traveling along the same medium. Recall, there is two types of interference; constructive and destructive.
• Sound is a pressure wave, which consists of compressions and rarefactions. The interference of sound waves causes the particles of the medium to behave in a manner that reflects the net effect of the two individual waves upon the particles.

WAVE INTERFERNCE

• If a compression (high pressure) of one wave meets up with a compression (high pressure) of a second wave at the same location in the medium, then the net effect is that that particular location will experience an even greater pressure. This is a form of constructive interference.
• If two rarefactions (two low pressure disturbances) from two different sound waves meet up at the same location, then the net effect is that that particular location will experience an even lower pressure. This is also an example of constructive interference.

WAVE INTERFERNCE

• Constructive and destructive interference occur when the waves are of the same frequency. In this section we will study what happens when sound waves have slightly different frequencies. This gives rise to a phenomenon called beats.
• Sound beats are the periodic and repeating fluctuations heard in the intensity of a sound when two sound waves of slightly different frequencies interfere with one another.

WAVE INTERFERNCE

• The sound changes from loud to softer, then loud again, and so on. The diagram below illustrates the wave interference pattern resulting from two waves with slightly different frequencies.

the beats

the beats

• The beat frequency is the rate at which the sound alternates from loud to soft and equals the difference in frequency of the two sounds. If two sound waves with frequencies of 440 Hz and 442 Hz interfere to produce beats, a beat frequency of 2 Hz will be heard.
• The human ear is only capable of hearing beats with small beat frequencies (e.g., 8 Hz or less).

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EXIT

1/5

What happens when two wave sources vibrate in phase, leading to a difference in path lengths that is zero or an integer number of wavelengths?

Constructive Interference

Destructive Interference

Both A and B

None of the above

EXIT

2/5

Under what condition does destructive interference occur when two wave sources vibrate in phase?

A difference in path lengths of 1/4 wavelength

A difference in path lengths of 3/4 wavelength

A difference in path lengths of 1/2 wavelength

A difference in path lengths of a full wavelength

EXIT

3/5

When two or more waves are present simultaneously at the same place, what is the disturbance?

The sum total of the disturbances from the individual waves

The disturbance of the wave with the higher amplitude

The average disturbance of all the waves

The disturbance of the wave with the lower frequency

EXIT

4/5

What occurs when two rarefactions (low-pressure disturbances) from two different sound waves meet up at the same location in the medium?

Constructive Interference

Both A and B

Destructive Interference

No interference occurs

EXIT

5/5

What phenomenon arises when two sound waves with slightly different frequencies interfere with each other, leading to periodic and repeating fluctuations in the intensity of the sound?

Beats

Rarefaction

Standing Waves

Compression

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