Sound Waves

Sound waves as longitudinal wave

• In longitudinal waves, the character debris of the medium circulate in a direction parallel to the path of propagation of the disturbance
• The debris do not drift from one location to another, but they certainly oscillate backward and forward about their function of rest
• Sound waves propagate in a comparable way; therefore, sound waves are longitudinal waves

Transverse wave:

• A transverse wave is the only in which the individual particles of the medium flow approximately their endorse positions in a course perpendicular to the direction of wave propagation
• In a transverse wave, particles do not oscillate alongside the route of wave propagation, however, oscillate up and down about their advocate function because the wave travels

Characteristics of a Sound wave:

• Crest and trough: In a wave, a top is referred to as the crest and a valley is called the trough
• Wavelength: It is the gap between continuous compressions (C) or two continuous rarefactions (R)which can be represented via λ (Greek letter lambda),its SI unit is metre (m)
• Oscillation: The change in density from the high charge to the high cost, but to the highest  rate, to make one complete oscillation
• Frequency: It is represented by means of ν (Greek letter, nu). Its SI unit is hertz (image, Hz)
• Time period of the wave: it is the time taken through  consecutive compressions or rarefactions to go a set thing
• Its miles are represented via the manner of the photograph T, and its SI unit is 2nd (s)
• Frequency and term are related as follows:

ν = 1T

• Pitch: The faster the movement of particles of the source (or object which is producing sound), the higher is the frequency and the higher is the pitch
• Amplitude of the wave: It is the magnitude of the maximum disturbance (clashing of particles) in the medium on either side of the mean value, its unit is that of density or pressure

• The hardness(you can also say loudness) or softness(or you say sweet voice) of a sound is determined basically by its amplitude

• A sound wave spreads out from its source, as it goes further from its source you will listen to less sound because its amplitude, as well as its loudness, decreases

• Quality or timber of sound: It helps to distinguish one sound from another having the same pitch and loudness

• The sound, which is more pleasant to hear as compared to others, is said to be of a rich quality
• A sound of a single (or you can say 1 or unity)  frequency is called a tone
• The pleasant sound produced due to a mixture of several frequencies (so many sounding mixing with each other) is called a note
• Noise(disturbance) is unpleasant to the ear
• Intensity of sound: It is the amount of sound energy (number of frequency or you can say number of cycles passess through)  passing each second  through the unit area (you can say point)

Speed of sound in different media

• Sound propagates (vibrates) through a medium(or you can say in common term object) at a finite speed
• The speed of sound depends on the properties of the medium(particular object) through which it travels
  • The speed of sound decreases from solid (include metal,non metal) to gaseous state (air)
  • Within a medium, the speed of sound increases with an increase in temperature(if you increase temperature molecules gain kinetic energy, it makes them collide to each other more fast and more impactful)

Sonic boom

• At the point when the speed of any article crosses the speed of sound, it is supposed to go at supersonic speed 
• Sound travelling at a supersonic speed produces shock waves in air that convey a lot of energy enough to break window glass and even harm buildings
• The pneumatic force variety related with this sort of shock waves creates a very sharp (like you will feel squeezing sensation in your by hearing it) and boisterous sound called the “Sonic boom”

Reflection of Sound

The law of reflection of sound describes that the directions in which the sound is incident (touching object) and reflected (after touching that object bounceback) make equal angles with the normal to the reflecting surface at the point of incidence, point of reflection and normal (dividing line between incident line and reflected line) line lie on the same plane.

Echo: Echo is the reflection(repetition) of sound that arrives at the listener with a delay after the direct sound.

• The sensation of sound processes and sends to our brain for about 0.1 s
• To hear an echo easily, the time interval between the original sound and the reflected sound should be at least 0.1s
• The total distance covered by the sound from the point where it is created to the reflecting surface and back should be at least:

344 m/s × 0.1 s = 34.4 m (here, 344 m/s is the speed of sound)

• For hearing echoes impeccably, the reciprocal distance of the hindrance from the source of sound must be half of this distance, that is,17.2m.
• This distance changes with varying temperature of air
• Echoes can be heard more than one due to multiple and successful reflections
• The roaring of thunder can be heard by the person due to successful reflection on multiple surfaces

Reverberation: It is the repeated reflection of sound that results in making sound impactful. 

Uses of multiple reflection of sound

• Stethoscope, a medical instrument used by doctors for listening to sounds produced within the body, mainly in the heartbeat or lungs
• Generally, the ceilings of musical halls, conference halls, and cinema halls are twisted so that sound (after touching the ceiling gets reflected) reaches all corners of the hall

Conclusion

Sound waves are characterized by the movement of particles within the medium, which are known as mechanical waves.Sound can’t move  through vacuum because there are no particles to vibrate.Every year questions from sound waves are asked in UPSC prelims and mains. So, UPSC aspirants must do a good preparation over one/ two  years to score high marks in this section. Air is the most common  medium through sound travels.While a vibrating object moves in advance, it pushes and compresses the air within the front of it, developing a location of immoderate stress. This vicinity is referred to as a compression (C). This compression starts off evolving to move a long way from the vibrating item, and even as the vibrating item moves backwards, it creates a region of low strain referred to as rarefaction (R). Because the item moves backward and forward hastily, a chain of compressions and rarefactions is created inside the air. Those make the sound wave that propagates via the medium. Greater density of the particles within the medium gives greater stress and vice versa. Therefore, propagation of sound can be visualized in vibrating in density versions or pressure versions in the medium.