Nature and characteristics of sound waves - class-IX

Sound travels as mechanical waves. A mechanical wave is a disturbance that moves and transports energy from one place to another through a medium. In sound, the disturbance is a vibrating object. And the medium can be any series of interconnected and interactive particles. This means that sound can travel through gases, liquids and solids.

It is a conceptual and memory based question.

A pure sine wave with a certain frequency is called tone.
option "C" is correct.

These waves are also called as shock waves, which are of conical shape when, a supersonic air craft moves faster than sound.

Quality is used to describe the quality of the waveform as it appears to the listener. Therefore,  the quality of a note depends upon the waveform. 
Two notes of the same pitch and loudness, played from different instruments do not sound the same because the waveforms are different and therefore differ in quality or tone.

Quality is used to describe the quality of the waveform as it appears to the listener. Therefore,  the quality of a note depends upon the waveform. 
Two notes of the same pitch and loudness, played from different instruments do not sound the same because the waveforms are different and therefore differ in quality or tone.
Hence, quality of the sound is affected due to the change in its waveform.

Shocks are caused by objects moving faster than the speed of sound in the medium.
(The shock tries to bring the velocity of the fluid in the medium to subsonic).

Sound waves are not transmitted to long distance because they are absorbed by the atmosphere. 

Frequency of the wave is the property which depends on source.

Time required to complete one vibration is T secs

In one full vibration, the particle covers a total distance of 4A

Thus, time required to cover a total distance of 4A during one vibration is T secs or 1 Time period

The correct option is (a)

Using the formula v = f * lambda, where v = 330 m/s and lambda = 110 cm = 1.1 m. Thus, f = v / lambda = 330 / 1.1 = 300 Hz.

The hertz (symbol Hz) is the unit of frequency in the International System of Units (SI). It is defined as one cycles per second.

On increasing the stretching force on a wire in a guitar, the frequency also increases.

The intensity or loudness of sound depends upon  ,

The walls of the auditorium should be equipped with good absorbing material , otherwise sound waves coming back after reflection from different walls may produce interference , constructive interference at any place in auditorium will produce a loud sound whereas distructive interference at any place in auditorium will produce a faint sound , making the music unpleasant . 

When we change amplitude of vibration , volume of the sound also changes and due to volume of sound loudness will also change .

The loudness of sound depends on amplitude of vibration of the source. Loudness of sound is directly proportional to the square of the amplitude of vibration producing the sound.

The amplitude of a sound wave determines its loudness. Sound wave with a large amount of energy have a larger amplitude which increases the loudness in the wave. A large amplitude means a louder sound and a smaller amplitude means a softer sound.

Louder the sound more is the amplitude of vibrating body

Intensity of sound is an objective quantity. It does not depend on the response of our ears. 
Loudness is a subjective quantity. It cannot be measured as a physical quantity.

Megaphone is based on multiple reflection of sound. It is a horn shaped tube designed to send amplified sound in a particular direction. It is also called Loud hailer.

Intensity of sound is an objective quantity. It does not depend on the response of our ears. Loudness is a subjective quantity. It cannot be measured as a physical quantity.

In humans sound is produced by the vioce box or larynx. It is the upper part of the wind pipe. Two vocal cords are stretched across the voice box leaving a narrow slit. When the lungs force air through the slit, it vibrates and produces sound.

Loudness of the sound  $L = 10 \log _{10} \dfrac{I}{I _o}$

Loudness of sound is proportional to the intensity and amplitude of sound. So when we turn on the volume of tv, the amplitude of sound wave increases hence, loudness of sound increases 

Loudness that we sense is related to the intensity of sound. 

The natural frequency of vibration of a system is commonly referred to as the eigenfrequency or eigentone in acoustics and mechanics.

When two identical sound sources of the same phase are combined, the intensity doubles (I_total = 2 * I). The change in decibels is 10 * log10(I_total / I) = 10 * log10(2) = 10 * 0.3 = 3 dB. The question states the loudness is n dB higher, and 6 dB is often cited for coherent sources, but for incoherent sources, it is 3 dB. Given the options, 6 dB is likely expected if the sources are coherent.

The change in sound intensity level in decibels is calculated using the formula delta L = 10 log10(I2/I1). Given that the intensity increases by a factor of 10^5, substitute this into the formula to get 10 log10(10^5) = 10 * 5 = 50 dB. Therefore, the increase in the intensity level is 50 db.

The sound level of N identical independent sources each at level L is given by the formula L_total = L + 10 log10(N). Here, N = 100 students and each shouts at 100 dB. Calculating the addition gives 100 + 10 log10(100) = 100 + 10 * 2 = 120 dB.

Loudness depends on the square of the amplitude of the wave. 

When a sound gets louder , its amplitude increases , as intensity $I\propto A^{2}$ (amplitude) , therefore intensity of sound also increases , which in turn increases level of intensity i.e. decibel .

Increased frequency means decreased wavelength and higher pitch/ sharpness. So increase in frequency makes sound more sharper while higher amplitude or higher intensity makes louder sound. 

when the tuning fork is held in hand there is only air in contact to the fork and sound waves force the air particles to vibrate but when the fork is in contact with the table the sound waves will travel in table as well as air which is in contact with table top. The sound dies sooner as the waves travel much faster in solids and liquids than in gases.

The sound level difference in dB is 20 * log10(P2/P1) for pressure amplitude. Given 30 dB = 20 * log10(ratio), then log10(ratio) = 1.5, so the ratio is 10^1.5, which is approximately 31.62, rounding to 32.

Pitch depends on string length and string tension.

1. If the string's mass per unit length remains constant, for longer string, high tension will produce high pitch.
2. If the string's length remains constant, for heavier string, the higher the tension will generate higher pitch.

The pitch of sound increases if its frequency increases. 
Pitch describes how high or low a tone is and depends upon the rapidity with which a sounding body vibrates, i.e., upon the frequency of vibration. The higher the frequency of vibration, the higher the pitch.

In figure B , wavelength (distance between two successive compressions or rarefactions ) is large therefore frequency will be smaller i.e. pitch is low .

The frequency determines the shrillness or pitch of a sound. If the frequency of vibration is higher, we say that the sound is shrill and has a higher pitch. If the frequency of vibration is lower, then we say that the sound has low pitch.

As the frequency of vibration of an object increases, the pitch or shrillness of sound produced by it also increases.

The characteristic of sound which distinguishes between a sharp sound and dull sound is called pitch

 Pitch is the characteristic of a wave by which sound wave appears shrill or grave. It depends upon the frequency of the wave. 

a shrill sound has a high pitch and a dull sound has a low pitch .

The vocal cords of women are thicker than men , therefore they produce a shrill sound , which we know has higher frequency or higher pitch , whereas men's voice is grave , means low frequency i.e. lower pitch .