Science M.C.Q. [1 M]

This is because the screams are ultrasonic $($above $20,000$ hertz$)$ which the human ear cannot hear as humans can only hear the sound in the range of $20\ Hz − 20,000\ Hz.$

$30,000Hz$
Sound having a frequency of more than $20000Hz$ in known as ultrasonic. It can not heard by us.

The speed of water in sound is $1530m/s.$

The sound which is produced due to a mixture of several frequencies is called a note and it is pleasant to listen too. An octave consists of eight different note, ranging from $256Hz$ to $512Hz.$

The approximate value for the speed of sound in air is $344\ m/ s.$
Distance $= 300\ m$
Speed $= 5000\ m/ s$
$\therefore$ $\text{Time taken}=\frac{\text{Distance}}{\text{Time}}$
$=\frac{300}{5000}$
$=0.06\text{s}$

$SONAR$ uses ultrasonic sound waves.

given,
height, $s = 500m$
$g = 10$
Speed of sound $= 340$
On analysing we get that we have to find time period
first analyze the data and apply different formulas for it then see which formula suits the best. The formula that should be used here is
$\text{s}=\text{ut}+\frac{1}{2\text{at}^2}$
$\text{u}=0$
$500+1+\frac{1}{2}\times10\times\text{t}\times\text{t}$
We get $t = 10\ sec$
Now the time for the resound $=\frac{500}{340}=1.47\text{sec}$
Total time $= 10 + 1.47$
$= 11.47\ sec$

The frequency $(f)$ of a wave is the number of full wave forms generated per second. This is the same as the number of repetitions per second or the number of oscillations per second.
In this case, an object attached to one end of a spring makes $20$ vibrations in $10 s.$ That is, $20$ vibration in $10$ seconds. S in one second it makes $2$ vibrations.

Time taken to list the sent signal is $0.4s.$
Speed of sound in water is $1,500\ m/s.$
So,
$=\frac{1500\times0.4}{2}$
$=300\text{m}$

Sound travels faster in liquids than in gases because molecules are more tightly packed. In fresh water, sound waves travel at $1,482$ meters per second $($about $3,315\ mph).$ That's well over 4 times faster than in air. In fact, sound waves travel over $17$ times faster through steel than through air.

The ultrasound waves can penetrate into matter to a large extent because they have very high frequency. They have frequency greater than $20,000\ Hz.$

Some of the elephant's vocalizations are infrasonic, and thus are inaudible to humans. The prominence of very low frequencies in the vocalizations is a defining characteristic of all three species of elephants. Sounds are generally considered to be infrasonic if their frequency is less than $20Hz ($the lower limit of human hearing$).$ Low frequency sounds travel farther than high frequency ones, which make them ideal for long distance communication.

At room temperature, the minimum distance for echo is $17.2m.$

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

Light waves, heat waves, $X-$rays are examples of electromagnetic waves, which do not require any medium for their propagation.
Sound waves cannot travel through a vacuum. It needs a material medium for its propagation. Sound waves can propagate only when the vibrational energy of the particles of the medium is travelling from one point to another.

The number of cycles per unit time is known as frequency. The SI unit of frequency is Hertz $(Hz).$

A vibrating body vibrates the surrounding air, and when these vibrations reach our ears we hear sound. But, some vibrations cannot be perceived as sound to humans as human ears can only detect sound in the frequency range of $20Hz$ to $20,000Hz,$ so depending upon the vibration frequency, can only we define a vibration as sound.

Frequency of $1\ Hz$ implies to $1$ complete vibration per second. This means, $60$ complete vibrations in $60$ second, or, in $1$ minute.

Audible sound has a frequency range of $20\ Hz$ to $20\ kHz.$
Infrasonic frequency is below audible range, i.e. below $20\ Hz.$
Ultrasonic frequency is above audible range, i.e. above $20\ KHz.$

An earthquake produces infra-sound before the main shock wave. Infra-sound is a low-frequency sound. It is sound that is lower in frequency than $20\ Hz$ (hertz) or cycles per second, the normal limit of human hearing. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infra-sound, the sound pressure must be sufficiently high.
Rhinos have extremely good ears, picking up infra-sound far deeper than the range of human hearing.
Rhinos can hear down to a frequency of four hertz, whereas even a human baby, with entirely undamaged ears, can normally only pick up sounds as low as $20\ hertz.$ Giraffes and elephants can also hear in this infra-sound range.

$d=?$
$\mathrm{v}=3 \times 10^8 \mathrm{~ms}^1$
$\mathrm{t}=2 \times 10^{-5} \mathrm{sec}$
$\text{d}=\frac{\text{v}\times\text{t}}{2}$
$\text{d}=\frac{3\times10^8\times2\times10^{-5}}{2}$
$=3\times10^3\text{m}$

Frequency is defined as the number of oscillations in one second , as the given object is oscillating, 50 times in one second therefore its frequency is $50\ Hz .$

$SONAR$ is a device that uses ultrasonic waves to measure the distance, direction and speed of under water objects.

The number of cycles an oscillator completes in each second is called its frequency.
The frequency $(f)$ of a wave is the number of full wave forms generated per second.
This is the same as the number of repetitions per second or the number of oscillations per second.

 $\text{v}=\frac{2\text{d}}{\text{t}}$
$\Rightarrow\text{v}=\frac{2\times640}{4}=320\text{m/ s}$
$\therefore\text{v}=\frac{2\text{d}}{\text{t}}$
$\Rightarrow320=\frac{2\text{x}}{7}$
$\text{x}=1120\text{m}$
Distance $=1120+640$
$=1760\text{m}$

1. They can penetrate water to long distances $($because of their high frequency and very short wavelength$)$ unlike ordinary sound waves or infrasonic waves.
2. Sound of these waves do not get mixed with engine noises or other sounds made by the ship. So, no confusion arises as these waves are not audible by human ear.

Elephants can communicate using very low frequency sounds, with pitches below the range of human hearing. These low frequency sounds$($frequency less than $20\ Hz),$ termed infrasonic sounds, can travel several kilometers, and provide elephants with a private communication channel that plays an important role in elephants complex social life. Their frequencies are as low as the lowest notes of a pipe organ.

Adult humans can hear from $20\ Hz$ to $20000\ Hz$ of frequency. Sound with frequency lower than $20\ Hz$ are called infrasonic, and higher than $20000\ Hz$ are called ultrasonic or supersonic which are inaudible to humans.

Infra-sound is a low-frequency sound. It is sound that is lower in frequency than $20\ Hz$ or cycles per second, the normal limit of human hearing. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. The ear is the primary organ for sensing infra-sound, but at higher intensities it is possible to feel infra-sound vibrations in various parts of the body.

$SONAR -$ Sound navigation and ranging is a technique, that uses ultrasonic sound waves to navigate and to detect objects on or under the surface of water.

Time taken to complete one vibration is called is called time period $(T).$

Thick strings with large diameters vibrate slower and have lower frequencies than thin ones. That is, lower the pitch. A thin string with a $10$ millimeter diameter will have a frequency twice as high as one with a larger, $20$ millimeter diameter. This means that the thin string will sound one octave above the thicker one. Hence, notes of different frequencies can be produced by vibrating different strings with different diameters.

Because the tuning fork is in resonance with air column in the pipe closed at one end, the frequency is
$\text{n}=\frac{\big(2\text{N}-1\big)\text{v}}{4\text{l}}$ where $N = 1, 2, 3$

Sounds having frequency more than $20,000\ Hz$ are called Ultrasonic sound. As this is above the normal hearing range for humans, we cannot hear ultrasonic sound.

The depth of an ocean is estimated by a device, called $SONAR,$ which sends ultrasonic waves towards the bottom of ocean , and after reflection, waves come back to the sonar. The time is recorded between the emitting and the receiving waves and having the speed of waves in water , we get the depth of ocean.

The acronym $SONAR$ stands for SOund Navigation And Ranging. Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects.

A first assumption to simplify the calculation is that light reaches you almost instantaneously (since it is almost a million times faster than sound). The time elapsed between watching and hearing the thunder, in this case, is the time taken by the sound to travel the distance.
$x = 10s × 340m/ s$
$= 3400m$

Frequencies higher than $20\ kHz$ are called ultrasonic sound or ultrasound. The property of ultrasonic waves in manufacturing emulsion for photographic films in its high frequency.

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. So $5\ Hz$ is infrasonic.

Ultrasound is an oscillating sound pressure wave with a frequency greater than the upper limit of the human hearing range. Ultrasound is thus not separated from normal (audible) sound by differences in physical properties, only by the fact that humans cannot hear it. Although this limit varies from person to person, it is approximately $20,000$ hertz in healthy, young adults. Ultrasound devices operate with frequencies from $20\ kHz$ up to several gigahertz.