A sound wave can be described by its :
• Frequency
• Amplitude
• Speed
1. Compression (C) – These are the regions where particles are crowded together and are represented by the upper portion of the curve that is known as the peak.
• The region of maximum compression is represented by its peak.
• Therefore, compressions are regions where density, as well as pressure, is high.
2. Rarefactions (R) - These are the regions where particles are spread apart and are represented by the lower portion of the wave curve that is known as the crest.
• These regions always have lower pressure.
• The trough of a wave is known as the valley and a peak is called the crest.
3. Wavelength - It can be well described as the distance between two consecutive compression (C) of two consecutive rarefaction (R).
• It is usually represented by the Greek letter lambda (λ).
• Its SI unit is metre (m).
4. Frequency (f) -
• It can be well described as the number of oscillations per unit time.
• It can also be described as the number of compressions + number of rarefaction (oscillation) per unit time.
• A complete oscillation can be described as the change in density from the maximum value to the minimum value and again to the maximum value.
Oscillation = rarefaction + compression
The SI unit of frequency was named as hertz in honour of Henry Rudolf Hertz.
• It is represented by (v).
• Its SI unit is Hertz having symbol (Hz).
5. Time period -
• It can be described as the time taken by two consecutive compressions or rarefaction to cross a fixed point is known as the time period of the wave.
• In other words, we can say that the time taken for one complete oscillation (compression + rarefaction) in the density of the medium is called the time period of the sound wave.
• Its SI unit is second (s).
• It is represented by the symbol (T).
We can relate frequency with time period :
\( v = { 1 \over T } \)
Or, \( T = { 1 \over v } \)
6. Pitch: When we hear two sounds at the same time, originating from different objects or instruments, traveling at same speed and through the same medium but we find both the sounds different. This is because of different characters of sounds which includes pitch.
• The faster the vibration of the source, the higher is the frequency and the higher is the pitch or, it is directly proportional to the frequency
• A man's voice is flat having low pitch while a woman’s voice is shrill having high pitch.
• It depends upon the size of the object, the type of the object and sound frequency.
7. Amplitude - It is described as the maximum displacement of the particle or the magnitude (value) of the maximum disturbance in the medium on either side of the mean value.
• It is represented by (A).
• Its SI unit is metre (m).
• It usually depends upon the force with which an object is made to vibrate, light force produce softer sound and vice versa, that’s why loudness and softness of a sound is basically determined by it.
8. Timber or quality – It is a characteristic that enables us to differentiate between two sounds even if they have the same pitch and loudness.
9. Tone – A sound having a single frequency is known as tone.
10. Note –
• A sound that has more than one frequency or we can say, a mixture of several frequencies is known as note.
• They are pleasant to listen.
11. Music - A sound that is pleasant to listen to and has a rich quality.
12. Noise - It can be described as an unpleasant sound.
13. Intensity of sound -
• It can be described as the amount of sound energy passing each second through a unit area or,
• A distance by which compression or rarefaction of the wave travels per unit time.
15. Loudness - It can be best measured by our ears. We may hear two different sounds of different intensity and still can decide which is louder.