Sound

A note of definite pitch is one where a listener can possibly (or relatively easily) discern the pitch.

Yes, the pitch will not change because loudness depends on amplitude and not the pitch. The pitch depends on the frequency of the sound. By hitting it hard it will make its amplitude higher. But the frequency will be same. And the point is to be noted is that the loudness depends on the amplitude not the frequency.

Sonar (originally an acronym for Sound Navigation and Ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water.

Ultrasonic waves: The waves with frequencies higher than 20,000Hz are termed as ultrasonics.

Sound travels through the air in the form of vibrations. These vibrations cause particles of air to compress together, creating disturbance and this causes the air around them to move in such a way that they are driven in waves away from the source.

With sound waves, amplitude is the extent to which air particles are displaced, and this amplitude of sounder sound amplitude is experienced as the loudness of sound.
Amplitude is directly proportional to the loudness of the sound.

As one wavelength = one crest + one trough,

half the wavelength = one crest or

one trough = AC (or CE).

Further, AC = AB + BC = BC + CD = BD (as AB = CD)

This is the reason why most probably animals are able to sense the earthquake much before its occurrence. And Also, the infrasound is used by the animals to communicate like rhinoceros and whale.

Infrasound, sometimes referred to as low-frequency sound, is sound that is lower in frequency than 20 Hz or cycles per second, the "normal" limit of human hearing.

The sitarist adjusts the frequencies of the sitar strings by adjusting the tension in them.

From the graph we get,

Time-period, T = 2 * 10^-6s.

Frequency is the number of wave cycles or revolutions per second. The formula for period (T) in terms of frequency is given by:

Frequency, √ = = 5 * 10⁵ Hz.

Wavelength Formula for any wave is given by:

Wavelength, λ =

Velocity of the wave = 1500 ms^-1

Therefore, λ = 1500 * 2 * 10^–6

= 3 * 10³ * 10^-6

= 3 * 10^-3 m

Graph (a) represents the male voice. Usually the male voice has less pitch as compared to female.

The faster the vibration of the source, the higher is the frequency and the higher is the pitch, as shown in fig. (b). Thus, a high pitch sound corresponds to more number of compression and rarefaction passing a fixed point per unit time.

In fig. (a), the vibration of the source is slower, the frequency is lower and therefore pitch is also lower.

To hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1 s.

If we take the speed of sound to be 344 m/s at a given temperature, say at 2^o C in air, the sound must go to the obstacle and reach back the ear of the listener on reflection after 0.1 s. Hence, the total distance covered by the sound from the point of generation to the reflecting surface and back should be at least (344m/s) * 0.1s = 34.4 m.

Thus, for hearing distinct echoes, the minimum distance of the obstacle from the source of sound must be half of this distance, that is, 17.2 m.

But in this case, the distance traveled by the sound reflected from the building and then reaching to the girl will be (6 + 6) = 12 m. That is, the minimum distance of the obstacle from the source of sound is 6 m, which is much smaller than the required distance (17.2 m). Therefore, no echo can be heard.

The audible range of sound for human beings extends for human beings extends from about 20 Hz to 20000 Hz, therefore, the sounds of frequencies below 20 Hz (called infrasonic sound or infra sound) are not audible and the sounds having frequencies higher than 20 kHz (called ultrasonic sound or ultrasound) are not audible to human beings.

The frequency of the vibration of the wings of a bee is much higher than the oscillations of a pendulum. Humming bees have the sound of higher frequency and it is in the audible range of sound for human beings.

If any explosion takes place at the bottom of a lake than the longitudinal waves will be produced.

Speed of sound = 340 ms^-1

Time = 10 s

Speed =

Distance = Speed * Time

= 340 * 10 = 3400 m

From the given figure,

We get, Angle of incidence = Angle of reflection

Thus, 50^o + x + x + 50^o = 180^o

2x + 100^o = 180^o

2x = 180^o – 100^o

2x = 80^o

x = 40^o

Therefore, Angle of reflection = 40^o

The ceilings of concert halls, conference halls and cinema halls are curved so that sound after reflection reaches all corners of the hall. Sometimes a curved soundboard may be placed behind the stage so that the sound, after reflecting from the sound board, spreads evenly across the width of the hall.

(i) Two sound waves having the same amplitude but different frequencies:

(ii) Two sound waves having the same frequency but different amplitude:

(iii) Two sound waves having different amplitudes and also different wavelengths:

Frequency and time period are related as follows: √ = (I)

We know, Speed, v =

v =

Here λ is the wavelength of the sound wave. It is the distance traveled by the sound wave in one time-period (T) of the wave.

Thus,

v = λ√ (From I)

That is, Speed = wavelength * Frequency

The speed of sound remains almost the same for all frequencies in a given medium under the same physical conditions.

(i) Given, Speed (v) = 340 m/s

Frequency (√) = 256 Hz

Wavelength (λ) =?

v = λ√

340 = 256λ

λ = 1.33 m

(ii) Given, Speed (v) = 340 m/s

Wavelength (λ) = 0.85 m

Frequency (√) =?

v = λ√

340 = √ (0.85)

√ = 400 Hz

Wavelength is the distance between two consecutive compressions or two consecutive rarefaction of a wave sound. Wave length is represented by Greek letter λ (lambda). The SI unit of wavelength is metre (m).

Time period is the time taken to travel the distance between any two consecutive compression or rarefaction from a fixed point. The time period of sound wave is represented by letter ‘T’. The SI unit of time period is second (s).