Sound Flashcards
When you strike the tuning fork on the rubber pad, it starts vibrating. These vibrations cause the nearby molecules to vibrate. Thus,
vibrations produce _______.
sound
Sound needs a material medium like air, water, steel ete for its propagation. It cannot travel through vacuum. This can be demonstrated by
the Bell - Jar experiment.
The waves that propagates with compressions and rarefactions are called
longitudinal waves.
In longitudinal waves the particles of the medium move to and fro along the direction of propagation of the wave.
A sound wave is an example of a
longitudinal mechanical wave
A sound wave can be described completely by five characteristics namely
amplitude, frequency, time period, wavelength and velocity or speed.
The maximum displacement of the particles of the medium from their original undisturbed positions, when a wave passes through the medium is called
amplitude of the wave.
Si unit meter
Denoted by A
Amplitude high. Sound loud
Amplitude low .. sound soft
The number of vibrations (complete waves or cycles) produced in one second is called
Frequency of wave
Denoted by n
Si unit of frequency is 1/s or hertz
Sound with frequency less than 20 Hz is called
Sound with frequency greater than 20,000 Hz is called
infrasonic sound.
ultrasonic sound
The time required to produce one complete vibration (wave or cycle) is called
time period of the wave.
It is denoted as T.
The SI unit of time period is second (s).
Frequency and time period are reciprocal to each other
The minimum distance in which a sound wave repeats itself is called its __________. In a sound wave, the distance between the centers of two consecutive compressions or two consecutive rarefactions is also called ________
wavelength
denoted as h (Greek letter, lambda). The SI unit of wavelength is metre (m).
The distance travelled by the sound wave in one second is called
velocity of the sound.
The SI unit of velocity of sound is ms^-1
Sounds can be distinguished from one another in terms of the following three different factors.
- Loudness
- Pitch
- Timbre (or quality)
The loudness of a sound depends on the
intensity of sound wave
Intensity is defined as
the amount of energy crossing per unit area per unit time perpendicular to the direction of propagation of the wave.
The unit of intensity of sound is decibel (dB).
The unit of intensity of sound is decibel (dB). It is named in honour of the Scottish-born scientist ________ who invented telephone
Alexander Graham Bell
_______ is one of the characteristics of sound by which we can distinguish whether a sound is shrill or base.
Pitch
High pitch sound is shrill and low pitch sound is flat.
________ is the characteristic which distinguishes two sounds of same loudness and pitch emitted by two different instruments.
Timbre
A sound of single frequency is called a tone and a collection of tones is called a _______.
Note
is then a general term for the distinguishable characteristics of a tone.
Timbre
The speed of sound
is defined as the distance travelled by a sound wave per unit time as it propagates through an elastic medium.
Speed =distance/time
= h/T
T=1/n
Speed v = nh. h lamda
Problem 1
A sound wave has a frequency of 2 kHz and wavelength of 15 cm. How much time will it take to travel 1.5 km?
v=nh
t =d/v
5 s
What is the wavelength of a sound wave in air at 20° C with a frequency of 22 MHz?
h=v/n
15.64μm
the sound travels with the speed which is much less than the speed of light
The speed of sound depends on the properties of the medium through which it travels.
The speed of sound is less in gaseous medium compared to solid medium In any medium the speed of sound increases if we increase the temperature of the medium.
For example the speed of sound in air is 330 ms¹ at 0 °C and 340 ms at 25 °C.
Aluminium at 25°c
Nickel
6420m/s
6040m/s
Steel
Iron
5960m/s
5950m/s
Brass
Glass
4700m/s
3980m/s
Water (sea)
Water (distilled)
1531m/s
1498m/s
Ethanol
Methanol
1207m/s
1103m/s
Hydrogen
Helium
1284m/s
965m/s
Air
Oxygen
Sulphur dioxide
340m/s
316m/s
213m/s
1) When the speed of any object exceeds the speed of sound in air (330 ms¹) it is said to be travelling at ______
1)supersonic speed
When an object travels at a speed higher than that of sound in air, it produces shock waves. These shock waves carry a large amount of energy.
The air pressure variations associated with this type of shock waves produce a very sharp and loud sound called the ‘sonic boom
Sound travels about ________ faster in water than in air. Since the speed of sound in sea water is very large (being about 1530ms which is more than 5500km/h), two whales in the sea which are even hundreds of kilometres away can talk to each other very easily through the sea water.
5 times
Reflection of sound
The angle in which the sound is incident is equal to the angle in which it is reflected,
Direction of incident sound, the reflected sound and the normal are in the same plane.
Uses of multiple reflections of sound
Musical instrument
Stethoscope
The sensation of sound persists in our brain for about
0.1s
for hearing distinct echoes, the minimum distance of the obstacle from the source of sound must be half of this distance Le. .
17 m
This distance will change with the temperature of air.
The total distance covered by the sound from the point of generation to the reflecting surface and back should be at least 340 m /s x 0.1
.
s = 34 m
A man fires a gun and hears its echo after 5s. The man then moves 310 m towards the hill and fires his gun again. If he hears the echo after 3s, calculate the speed of sound
v=310 ms^{-1}
The repeated reflection that results in this persistence of sound is called
reverberation
In an auditorium or big hall excessive reverberation is highly undesirable.
To reduce reverberation, the roof and walls of the auditorium are generally covered with sound absorbing materials like compressed fiberboard, flannel cloths, rough plaster and draperies. The seat materials are also selected on the basis of their sound absorbing properties
There is a separate branch in physics called _____ which takes these aspects of sound into account while designing auditoria, opera halls, theaters etc.
acoustics
______ are used in cars to alert deer to oncoming traffic so that they will not leap across the road in front of cars.
Ultrasonic whistles
An ______ is an image obtained by the use of reflected ultrasonic waves. It is used as a medical diagnostic tool. Ultrasonic sound is having application in marine surveying also.
echogram
Animals, such as _____, use echolation, an ultrasound technique that uses echoes to identify and locate objects
bats, dolphins, rats, whales and oil birds
____ can be used in cleaning technology. Minute foreign particles can be removed from objects placed in a liquid bath through which ultrasound is passed.
Ultrasounds
____ can also be used to detect cracks and flaws in metal blocks,
Ultrasounds
Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called
echo cardiography
Ultrasound may be employed to ______ formed in the kidney into fine grains. These grains later get flushed out with urine.
break small ‘stones’
SONAR stands for
Sound Navigation And Ranging.
_______ is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects
Sonar
Sonar consists of a transmitter and a detector and is installed at the _____
bottom of boats and ships
The distance of the object that reflected the sound wave can be calculated by knowing the speed of sound in water and the time interval between transmission and reception of the ultrasound
Echo ranging
2d/t=v
_________ technique is used to determine the depth of the sea and to locate underwater hills, valleys, submarines, icebergs etc
Sonar
ECG, the sound variation produced by heart is converted into electric signals.
Thus, an ECG is simply a representation of the electrical activity of the heart muscle as it changes with time
The sum of this electrical activity, when amplified and recorded for just a few seconds is known as an .
ECG
The outer ear is called ‘______. It collects the sound from the surroundings. The collected sound passes through the auditory canal.
pinna
At the end of the ear is eardrum or tympanic membrane. .
When a compression of the medium reaches the eardrum the pressure on the outside of the membrane increases and forces the eardrum inward. Similarly, the eardrum moves outward when a rarefaction reaches it. In this way the eardrum vibrates
The vibrations are amplified several times by three bones (__________) in the middle ear
the hammer, anvil and stirrup
In the inner ear, the pressure variations are turned into electrical signals by the _______
cochlea
A ship sends out ultrasound that returns from the seabed and is detected after 3.42 s. If the speed of ultrasound through sea water is 1531m s¹, what is the distance of the seabed from the ship?
2d = speed of ultrasound x time
2.618 km or 2618 m
Which of the following vibrates when a musical note is produced by the cymbals in a orchestra?
Metal plates
Sound travels in air:
if disturbance moves.
A musical instrument is producing continuous note. This note cannot be heard by a person having a normal hearing range. This note must then be passing through
a) wax
c) water
b) vacuum
d) empty vessel
Vacuum
The maximum speed of vibrations which produces audible sound will be in
a) sea water
b dry air
b) ground glass
d) human blood
Ground glass
The sound waves travel faster
a) in liquids
c in solids
b) in gases
d) in vacuum
In solids
Sound is a _______ wave and needs a
material medium to travel.
Longitudinal
Number of vibrations produced in one second
Frequency
The velocity of sound in solid is ______ than the velocity of sound in air
Greater
Vibration of object produces .
sound
Loudness is proportional to the
square of the Amplitud of Vibration
_______ is a medical instrument used for listening to sounds produced in the body.
Stethoscope
The repeated reflection that results in persistence of sound is called
Reverberation
The frequency of a source of sound is 600 Hz. Calculate the number of times it vibrates in a minute?
600*60
3600
A stone is dropped from the top of a tower 750 m high into a pond of water at the base of the tower. Calculate the number of seconds for the splash to be heard?
(Given g = 10 m s-² and speed of sound = 340 m s-¹)
time taken = 10 + 2.20 = 12.2s
