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Draw a curve showing density or pressure variations with respect to distance for a disturbance produced by sound. Mark the position of compression and rarefaction on this curve. Also define wavelengths and time period using this curve.

In propagation of sound, the particle of medium oscillate.
The time to complete one oscillation is called time period T.

Pitch is frequency of sound, which tells us number of oscillations, any particle will make in one second.

$f=\frac{1}{T}$

Distance between two consecutive crest or consecutive troughs is equal to wavelength of any sound.

Establish the relationship between speed of sound, its wavelength and frequency. If velocity of sound in air is 340 m s–1, calculate(i) Wavelength when frequency is 256 Hz.(ii) Frequency when wavelength is 0.85 m.

The wavelength of any sound is defined as distance travelled by disturbance in one time period of the oscillation of particle.

$\lambda=V \times T$

The number of oscillations per unit time is called frequency. Hence, frequency and time period are related as.

$f=\frac{1}{T}$

By putting the value of time period in the relation of wavelength, we will get:

$\lambda =\frac{V}{f}\Rightarrow V=f \times \lambda$

i) If frequency and sound velocity is given, wavelength can be calculated as:

$\lambda =\frac{V}{f}\\ \Rightarrow \lambda =\frac{340}{256}=1.328125m$

ii) If wavelength and sound velocity is given, frequency of sound can be calculated as:

$f=\frac{V}{\lambda }\\ \Rightarrow f =\frac{340}{0.85}=400Hz$

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Represent graphically by two separate diagrams in each case(a) Two sound waves having the same amplitude but different frequencies?(b) Two sound waves having the same frequency but different amplitudes.(c) Two sound waves having different amplitudes and also different wavelengths.

In propagation of sound, the particle of medium oscillates.
The time to complete one oscillation is called time period T.

Pitch is frequency of sound, which tells us number of oscillations, any particle will make in one second.

$f=\frac{1}{T}$

Distance between two consecutive crests or consecutive troughs is equal to wavelength of any sound.

By these information, we can draw the corresponding graphs.

Why is the ceiling and wall behind the stage of good conference halls or concert halls made curved?

The design of ceiling and wall in a good conference hall is to ensure proper sound at every seat of the conference hall.

This design is called acoustic design and design engineers are called acoustic engineers.

The ceiling and wall behind the stage are made curved, so that the reflected sound from them can reach to the audience evenly.

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For hearing the loudest ticking sound heard by the ear, find the angle x in the Fig.12.4.

Similar to light, sound also follows law of reflection.

If I sound is coming at an incident angle of $\angle i$ then it will go at the same reflection angle $\angle i=\angle r$.

In the given question, sound coming through the first pipe has angle of incidence equal to 40° that can be calculated as (90° - 50°)

The same sound will be reflected at an angle of 40°. Therefore, the second pipe has to be kept at the angle of 40° from normal.

Therefore the value of x will be 40°.

Sound produced by a thunderstorm is heard 10 s after the lightning is seen. Calculate the approximate distance of the thunder cloud. (Given speed of sound = 340 m s–1.)

The speed of light is very large in comparison with the speed of sound.

We can assume that lightning can be seen, without any time delay as light travels very fast.

If the sound produced by thunderstorm is heard 10 seconds after lightning that means sound took 10 seconds to reach from thundercloud.

As the speed of sound is 340 m/s, so distance travelled by sound in 10 seconds will be 3400 meters.

So the approximate distance of thunder cloud is 3.4 km.

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If any explosion takes place at the bottom of a lake. Infrasound type of shock waves in water will take place?

Transverse wave cannot travel in air or within the water.

Transverse wave can only travel at the surface of water or in solids.

So when any explosion takes place at the bottom of lake, the shock waves have to travel within the water.

These shock waves cannot be transverse and they have to be longitudinal waves like sound wave.

Why do we hear the sound produced by the humming bees while the sound of vibrations of pendulum is not heard?

The human ear can sense sound only if its frequency is more than 20 Hz and less than 20,000 Hz.

Sound of frequency less than 20 Hz is called infrasonic and a frequency more than 20,000 Hz is called ultrasonic.

The frequency of the disturbance created by humming bee is more than 20 Hz that’s why we can hear the sound.

Due to the vibration of pendulum, the frequency of disturbance is less than 20 Hz and we cannot listen the sound of vibration of pendulum.

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A girl is sitting in the middle of a park of dimension 12 m × 12 m. On the left side of it there is a building adjoining the park and on right side of the park, there is a road adjoining the park. A sound is produced on the road by a cracker. Is it possible for the girl to hear the echo of this sound? Explain your answer.

When we observe a sound directly or after reflection from any building, we call it an echo.

This echo can be heard or these two sounds can be distinguished, only if time gap between them is more than 0.1 second.

For this, separation between source and the wall must be more than 16 meter.

Assuming speed of sound = 320m/s

Distance between source and wall is d, then time to reach reflected sound will be:

$t=\frac{2d}{V}$

In the given case, the size of park is small. Therefore, it cannot cause any echo of the sound produced on the road.

Which of the above two graphs (a) and (b) (Fig.12.3) representing the human voice is likely to be the male voice? Give reason for your answer.

The difference between human male voice and female voice is on the basis of pitch or frequency.

Male voice will have lower frequency in comparison with female voice.

We know that frequency is inverse of time period of oscillation.

$f=\frac{1}{T}$

In the given graph, it is quite visible that time period of graph (a) is more than time period of graph (b).

Therefore graph (a)  must be corresponding to male voice.