Page 147 - Understanding NCERT Science 09

squeaks of the bat and know when a bat in construction of big structures like
is flying nearby, and are able to escape
capture. Rats also play games by
producing ultrasound.
Hearing Aid: People with hearing loss may
need a hearing aid. A hearing aid is an
electronic, battery operated device. The
hearing aid receives sound through a
microphone. The microphone converts the
sound waves to electrical signals. These
electrical signals are amplified by an
amplifier. The amplified electrical signals
are given to a speaker of the hearing aid.
The speaker converts the amplified
electrical signal to sound and sends to the
ear for clear hearing.
Q uestions
1. What is the audible range of the
average human ear?
2. What is the range of frequencies
associated with
(a) Infrasound?
(b) Ultrasound?
11.5 Applications of Ultrasound
Ultrasounds are high frequency waves.
Ultrasounds are able to travel along well-
defined paths even in the presence of
obstacles. Ultrasounds are used extensively
in industries and for medical purposes.
• Ultrasound is generally used to clean
parts located in hard-to-reach places,
for example, spiral tube, odd shaped
parts, electronic components, etc.
Objects to be cleaned are placed in a
cleaning solution and ultrasonic waves
are sent into the solution. Due to
the high frequency, the particles of
dust, grease and dirt get detached and
drop out. The objects thus get
thoroughly cleaned.
• Ultrasounds can be used to detect
cracks and flaws in metal blocks.
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Rationalised 2023-24
buildings, bridges, machines and also
scientific equipment. The cracks or
holes inside the metal blocks, which
are invisible from outside reduces the
strength of the structure. Ultrasonic
waves are allowed to pass through the
metal block and detectors are used to
detect the transmitted waves. If there
is even a small defect, the ultrasound
gets reflected back indicating the
presence of the flaw or defect, as shown
in Fig. 11.14.
Fig 11.14: Ultrasound is reflected back from the
defective locations inside a metal block.
Ordinary sound of longer wavelengths
cannot be used for such purpose as it will
bend around the corners of the defective
location and enter the detector.
• Ultrasonic waves are made to reflect
from various parts of the heart and
form the image of the heart. This tech-
nique is called ‘echocardiography’.
• Ultrasound scanner is an instrument
which uses ultrasonic waves for
getting images of internal organs of the
human body. A doctor may image the
patient’s organs, such as the liver, gall
bladder, uterus, kidney, etc. It helps
the doctor to detect abnormalities,
such as stones in the gall bladder and
kidney or tumours in different organs.
In this technique the ultrasonic waves
travel through the tissues of the body
and get reflected from a region where
there is a change of tissue density.
SCIENCE
Metallic components are generally used