Class 8, Science, Chapter-10, Lecture-2, Ultrasound (Notes)
CHARACTERISTICS OF SOUND:
- Loudness:
Loudness of sound is the measure of sound energy reaching the ear per second.
Loudness or softness of a sound wave is the sensation that depends upon its amplitude.
When we strike the top of a table with more force, it vibrates and produces a loud sound.
But, when we strike the top of a table with lesser force, the vibrating table top produces soft sound waves.
Louder sound has more amplitude. - Pitch:
Pitch is the sensation (brain's interpretation) of the frequency of an emitted sound.
The pitch of sound (shrillness or flatness) depends on the frequency of vibration.
A high pitch sound is called a shrill sound
A low pitch sound is called a hoarse sound or heavy sound - Quality or Timbre:
Quality or timbre of sound wave is that characteristic which helps us in distinguishing between two sounds of same loudness and same pitch.
MUSIC Vs NOISE:
Music is the sound that is pleasant to the ears and Noise is the sound that is unpleasant to the ears.
TONE Vs NOTE:
A pure sound of single frequency is called tone.
An impure sound produced by mixture of many frequencies is called a note. It is pleasant to hear.
LIGHT TRAVELS FASTER THAN SOUND:
- Man hears sound of thunder only after he sees the flash of lightning. This is because light travels at a very great speed as compared to the speed of sound, we see the flash before the sound.
- The flash of a gunshot reaches us before the sound of the gun shot. This is because light travels at a very great speed as compared to the speed of sound, we see the flash before the sound.
TYPES OF SOUND BASED ON FREQUENCY:
- Audible Range of sound
The sound between frequencies of 20 Hz to 20,000 Hz. is the audible sound. - Infrasound or Infrasonic sound
Sound, below the frequency of 20Hz is called infrasonic or infrasound. Infrasound is produced because of very slow vibration.
Example: Simple pendulum, Earthquakes.
Human being cannot hear infrasound.
Many animals such as whale, elephant, rhinoceros, etc. can produce and hear infrasound. - Ultrasound or Ultrasonic Sound
Sound, above the frequency of 20000 Hz is called ultrasound.
Example: Volcanic eruptions also produce ultrasound
Humans cannot hear the ultrasonic sound.
Animals such as dogs, cat, bat, monkey, deer can hear ultrasound.
Human children can also hear to ultrasound.
USES OF ULTRASOUND:
- Detection of any deformities (flaws, cracks) in metal blocks or sheets.
- Ultrasound is generally used to clean parts located in hard to reach places like spiral tubes.
- Ultrasound is used by bats to find their prey. Bats produce high-pitched ultrasonic squeaks. These high-pitched squeaks are reflected by objects such as preys and returned to the bat’s ear. This allows a bat to know the distance of his prey.
- Dolphins use ultrasound to find fish and to detect sharks that may attack them.
- Ultrasound may be employed to break stones formed in the kidneys into fine grains.
- Ultrasound scanner is used to detect problems of the internal organs.
- Ultrasonography is the process of getting the pictures of parts of the body by using multiple reflections.
- Echocardiography- is the use of ultrasound to detect activities of heart.
- Ultrasonography is used to study the development of foetus during pregnancy to detect any abnormalities.