DO YOU HEAR IT?
You might ask yourself a question most of the times? How much can we, as humans, hear? Well, here’s the answer.
Humans cannot hear anything outside their frequency range! Which is from 20Hz to 20KHz (20,000 Hz). We call this the “Audible Frequency Range Of Sound. Vibrations of this form are known as sonic vibrations or sound vibrations.
Sound frequencies which are less then 20 Hz (Hertz) are called Infrasonic sound and sound frequencies which are more than 20KHz/20,000Hz are called ultrasonic sound.
Dogs have much sharper hearing then humans as they can hear within the frequency range of 50 Hz-45 KHz!
Also, Bats can detect frequencies which are as high as 100,000 Hz/1,000 KHz !
WHAT PRODUCES SOUND IN ANIMALS?
Most mammals such as dogs, cows, cats etc. produce sound with the help of their vocal cords.
Dogs can be easily trained to respond to a whistle which generates ultrasonic vibrations!
This whistle is called as the Galton’s whistle.
Birds produce sound by a ringed cartilage which is known as Syrinx, which is fixed at the beginning of their windpipe. Some birds have 2 parts in the syrinx. Due to this, they can produce 2 different notes.
Insects such as bees, mosquitoes, houseflies produce a buzzing sound by rapidly flapping their wings, which indicates that insects don’t have any special sound-producing organs.
Dolphins are related to the whale family. They use ultrasonic sound to locate their prey.
USE OF ULTRASONIC VIBRATIONS IN INDUSTRY
- Ultrasonic vibrations are used for homogenising milk i.e. the milk is exposed to ultrasonic vibrations. These vibrations break down the larger particles of the fat in milk to smaller particles.
- Ultrasonic vibrations are used in dishwashing machines. In those type of machines, water (H2O) and detergent are vibrated with ultrasonic vibrators. Those vibrating detergent particles rub against the dirty utensils and thus clean them.
- Ultrasonic vibrations are used in an ultrasonography for diagnosis.
- Ultrasonic vibrations are also used in detecting flaws in metallic articles, flaws such as hidden cracks, voids (gap between particles) etc.
NOISE AND MUSIC
Noise is unpleasing to the ears while music is pleasing to the ears.
MEASURE OF LOUDNESS OF SOUND
The loudness of sound is measured in Decibels (dB). This signifies the sound pressure level.
Humans can pick up sounds from 10 dB to 180 dB
If a sound is between 50 dB and 60 dB, it is considered normal.
A normal human being can tolerate a sound till 80 dB.
A sound above 80 dB is painful to the ears and causes various health problems.
NOISE POLLUTION
The disturbance produced in the environment by undesirable, loud and harsh sound from various sources is called noise pollution.
Sounds like whispering which are from 10 dB to 25 dB is just audible to us
While on the other hand, sounds like that of a radio or a TV at low volume which is from 30 dB to 40 dB are known as “comfortable sounds”. These sounds are audible to us very easily and do not cause any harm.
The level of loudness of a normal conversation is from 50 dB to 60 dB. This sound is not really that loud, it is moderately loud though.
Automobiles and vehicles like cycles, cars produce a sound which ranges from 60 dB to 70 dB. This is where it gets loud!
Substances like a mixer grinder or the sound on a busy road crossing has a sound which varies from 70 dB to 80 dB. These are very loud sounds but are somewhat tolerable,
Automobiles like motorcycles, heavy vehicles like trucks, airplanes produce a sound that varies from 90 dB to 105 dB, This type of sound and above are termed as “noise”. They are very loud and very uncomfortable
Lightning, a natural phenomena produces a sound varies from 120 dB to 130 dB. This type of sound is very uncomfortable and even more loud.
Allas, a jet airplane produces a sound which varies from 130 dB and can be even louder. These types of sound are very painful sounds.
APPLICATIONS OF REFLECTION OF SOUND
SONAR (Sound Navigation And Ranging) is a device used in ships and submarines to locate obstacles such as icebergs, strong rocks, other submarines and ships etc. A SONAR can also be used for finding the depth of a sea/ocean.
Principle: It is based on the principle of the reflection of a sound wave/echo. A beam of ultrasonic waves from the transmitter of a SONAR is sent towards the bottom of the sea. This beam is reflected back from the bottom of the sea and is received by the receiver of the SONAR on the ship. The time taken for the ultrasonic wave to go from the sip to the bottom of the sea and back is noted.
Thus, the time taken by the ultrasonic waves to go from the ship to the bottom of the sea is t/2 seconds
S = v * t/2
where t = Time taken to come back to the ship after going from the ship to the bottom of the sea and back
S = depth of the sea
And V = speed of the ultrasonic wave in water.
