Effect Of Change In Frequency

Waves in general:

Every one of us, at some point in time, has tried to throw a pebble in a lake or any stagnant water body. Throwing a stone in water gives away a series of periodic motions on the water surface in concentric circles. These motions start at the point of contact. These movements are nothing but the water waves. 

Waves are the transmittance of the disturbances created at one point in a medium or object. These disturbances generate vibrational movement in the neighbourhood particles of the medium, and the energy of disturbance is hence carried forward away from the point of disturbance.  Here it should be noted that not the matter but only the energy of vibrating particles is transferred. The pattern of the vibrational motion set can be in the form of transverse waves or the form of longitudinal waves. Longitudinal waves traverse in the same direction as the vibrational motion of particles of the medium. Here the vibrations are just to and fro movement of particles about their original mean position. 

Basics of sound waves:

Scientifically sound is a kind of wave. A sound wave is categorized as a progressive longitudinal wave. When an object is set into oscillations, by any action like our vocal cords when we speak, tuning forks after a jerk, etc., set consecutive particles of the medium into vibrational motion. This is the sound wave or acoustic wave. Sound waves give rise to periodic pressure differences in the medium and are propagated as a series of alternate compressions and rarefactions.  

Sound waves are mechanical waves. This means that the presence of some medium is the prerequisite for the successful propagation of sound waves. Generally, this medium is air. The nature of the medium and its other characteristics affect the propagation of sound waves. 

Sound waves are characterized with the help of their characteristic physical properties like all other waves. Here are given these features one by one:

1.Amplitude:

In sound waves, since they are longitudinal waves, the vibrational motion of particles of the medium is definite to and fro motion of particles about their original mean position. The maximum distance covered by the vibrating particle in either direction is known as the amplitude of the wave. Each molecule of medium propagating the sound wave has equal amplitude. Amplitude is measured in meters in the SI system. 

2.Period (T):

The time taken by one particle to complete one vibration is known as a period. SI unit of a period is second. 

3.Frequency (n):

The number of vibrations completed by a particle in the time of one second is called the frequency of the sound wave. For sound waves, the SI unit of frequency is hertz (Hz).

4.Wavelength (λ):

The distance between two consecutive compression or rarefactions is known as the wavelength of the sound wave. 

5.Velocity (v):

The distance covered by the wave in one second is called the velocity of the sound wave. 

These are physical and scientific characteristics of a sound wave. But in day-to-day life, we perceive and distinguish various sounds based on their properties like loudness, intensity, and pitch. All these general properties are, in effect, the function of the above mentioned physical characters of the sound wave. In the following section, we will learn about interrelation in the different characteristics of sound waves. 

Correlation between the different parameters of sound waves:

1.The loudness of sound:

Loudness describes the energy of a sound wave when the frequency of the wave is constant. The energy of vibrations of particles carrying the sound waves is the product of squares of their frequency and amplitude. When the frequency of two sound waves is identical, their energy differs due to differences in the amplitude of the waves. This describes the loudness of the sound. The more the amplitude of particular vibrations, the louder the sound is. 

Since we know that propagation of sound as a series of compression and rarefactions decapitates some energy as heat, this causes a decrease in the relative amplitude of particles as the sound wave progresses over a long distance. This means that as the sound wave travels over long distances, its loudness decreases as compared to that at the point of disturbance. 

2.Pitch of a sound:

The Pitch of a sound is its characteristic that we detect and perceive and distinguish the quality of sound. Pitch is dependent completely on the frequency of the sound wave. The greater the frequency of the sound the higher is the pitch. 

The Pitch or frequency of the sound is a very important and fundamental characteristic of the sound. Different living beings are sensitive to different pitches of sound. For example, elephants can detect very low pitch sound in the infrasound range, which comes in the range of 0-20 Hz. We, humans, are sensitive to sounds of pitch 20-20000 Hz. This range is known as the auditory field. Dolphins and bats have a very broad range of sensitivity to sounds. They can detect sound waves in the range of 20 to 160,000 Hz!

Velocity, wavelength, and frequency:

As stated above, the velocity of a sound wave is the distance covered per second. As we know, a sound wave travels a distance of its wavelength in one period thus velocity can be given as-

v=λ  ⁄ T

But T is reciprocal of frequency, hence, 

v=nλ

Conclusion:

Sound is nothing but a type of wave. Sound waves are characterized as mechanical, longitudinal progressive waves. Sound waves, on the scientific side, are described by their properties as amplitude, frequency, wavelength, and speed. In practical life, we distinguish sound based on its loudness, pitch, and quality. But these general characteristics of the sound waves are also functions of their physical properties. Studying the correlation between these properties is very important for analyzing sound waves. Loudness is related to the amplitude, while pitch is related to the frequency of the sound wave.