Reflection of Sound Waves and Echoes Flashcards
When is sound produced?
Sound is produced when a body vibrates and it reaches us through the vibrations of the particles of the surrounding medium
What does sound need for its propagation?
A medium
State two factors on which the speed of a wave travelling in a medium depends
- Elasticity of medium
2. Density of medium
What is the audible range of frequency?
The range of frequency from 20 Hz to 20,000 Hz to which our ears our sensitive
Why does the audible range of frequency of old people decrease?
The hearing sensitivity for ears falls for both high and low frequencies
What is ultrasonic sound?
The sound of frequency above 20,000 Hz
What is infrasonic sound?
The sound of frequency below 20 Hz
What is the speed of ultrasonic and infrasonic sound?
Same as that of audible sound
Define amplitude of a wave
The maximum displacement of the particle of the medium on either side of its mean position, is called the amplitude of the wave
Define time period of a wave
The time taken by the particle to complete one vibration is called the time period of the wave
Define frequency of a wave
The number of vibrations made by the particle of the medium in one second, is called the frequency of the wave
Define wavelength of a wave
The distance travelled by the wave in one time period of vibration of the particle of the medium, is called the wavelength (λ)
Define wave velocity of a wave
The distance travelled by the wave in one second is called the wave velocity of the wave (V)
How are V, f and λ related?
V = fλ
How are time period and frequency related?
f = 1/T
What do the frequency and time period of a wave depend on?
The vibrating source producing the sound
What do the velocity of the wave and hence its wavelength depend on?
The properties of the medium in which the wave travels
Give another name for sound waves
Mechanical or elastic waves
Why are sound waves called mechanical waves?
When the medium particles vibrate, there is a change of KE into PE and vice versa, so sound waves are called mechanical
Name the two kinds of mechanical waves
- Longitudinal waves
2. Transverse waves
When is a wave called a longitudinal wave?
If the vibrations of the medium particles are along the direction of propagation of the wave, thus forming compressions and rarefactions in the medium, the wave is called a longitudinal wave
Give examples of longitudinal waves
Sound waves in air, in soil and inside a liquid
In which media can longitudinal waves travel?
Solid, liquid and gas
When is a wave called transverse wave?
If the medium particles vibrate normal to the direction of propagation of the wave, forming crests and troughs, the wave is called a transverse wave
In which media are transverse waves formed?
In media which possess rigidity and that’s why they can only travel in solids and on the surface of liquids
How are electromagnetic rays formed?
Formed by the periodic vibrations of the mutually perpendicular electrical and magnetic fields in a plane normal to the direction of wave propagation
What type of waves are electromagnetic waves?
Transverse
In which form do electromagnetic waves transfer energy?
In the form of photons
Give one difference bet. sound waves and electromagnetic waves in terms of media of travel
Sound waves cannot travel in vacuum, electromagnetic waves can
Differentiate between light waves and sound waves on the basis of nature of the wave
Sound waves are mechanical waves, whereas light waves are electromagnetic waves
Differentiate between light waves and sound waves on the basis of speed
Sound waves have low speed (330 m/s in air), whereas light waves have high speed (3*10^8 m/s in air)
Differentiate between light waves and sound waves on the basis of wavelength
The wavelength of light waves is very small. of the order of 10^-6 m, whereas the wavelength of sound waves is in the range of 10^-2 m to 10 m
Differentiate between light waves and sound waves on the basis travel
Light waves are transverse, whereas sound waves are longitudinal in air
Define reflection of sound wave
The return of a sound wave on striking a surface such as wall, metal sheet, plywood, etc. back in the same medium is called the reflection of sound wave
Does the texture of the surface depend in reflection of sound waves?
Sound waves get reflected from any surface, whether smooth or hard; polished or rough
What is the only requirement for reflection of a sound wave?
The size of the reflecting surface must be bigger than the wavelength of the sound wave
What is the phenomenon of reflection of sound waves utilized in the making of?
A megaphone, speaking tube, ear trumpet or sound board
Define echo
The sound heard after reflection from a distant obstacle (such as a cliff, hillside, wall of a building, edge of a forest) after the original sound has ceased, is called the echo
What is the condition for hearing an echo?
An echo is heard only if the distance of the person producing a sound from the rigid obstacle (or reflector) is far enough to allow the reflection sound to reach the person at least 0.1 second after the original sound is heard
Why must the echo reach the person at least 0.1 second after the original sound is heard?
The sensation of sound persists in our ears for about 0.1 second after the exciting stimulus ceases to act
What should be the minimum distance between the reflecting surface in air and the listener to hear the echo distinctly?
17m
d = (340 * 0.1)/2
Define reverberation
If there are repeated reflections at the reflecting surface, the sound gets prolonged. This effect is known as reverberation
Where is reverberation experienced?
Hight tombs like Taj Mahal, Sikandra etc.
Name the three conditions for an echo to be heard distinctly
- The minimum distance between the reflector in air and the observer must be 17 m
- The size of the reflector must be large enough as compared to the wavelength of the sound wave
- The intensity of sound should be such that the reflected sound reaching the ear is sufficiently loud to be audible
How to determine the speed of sound by the method of echo?
V = total distance travelled/ time interval = 2d/t m/s
Give the three properties of ultrasonic waves for their wide use
- They can travel undeviated through a long distance
- They can be confined to a narrow beam
- They are not easily absorbed in a medium
Name the three properties not possessed by audible sound waves
- They can travel undeviated through a long distance
- They can be confined to a narrow beam
- They are not easily absorbed in a medium
Bats can produce and detect sound up to what frequency?
About 100 kHz
What is the speed that bats fly with?
With a speed much lower than the speed of sound
How is echo used in sound ranging by bats?
The sounds produced by the flying bats get reflected back from an obstacle in front of them. By hearing the echo, bats come to know, even in the dark, the location of the obstacle, so they turn away from their path and fly safely without colliding.
Define sound ranging
The process of detecting an obstacle is called sound ranging
What do dolphins use for hunting their prey?
Ultrasonic waves
How do fishermen or trawlers benefit from sound ranging?
He sends an ultrasonic pulse from a very high frequency vibrator into the sea and receives the pulse reflected back from the shoal of fish in a detector. The total time t of the to and fro journey of the pulse is recorded. The distance d of fish is then calculated by using d = Vt/2 where V is 1400 m/s
Who gets benefitted from sound ranging?
Fisherman or trawlers, dolphins and bats
What does the word SONAR stand for?
Sound navigation and ranging
What is echo depth sounding?
The process of finding the depth of the sea using the principle of a sonar in which ultrasonic waves are sent in sea water in all directions from the ship. These waves are received after reflection. To find the distance between obstacle and ship, d = Vt/2 is used.
Give the full form of radar
Radio detection and ranging
Which method is used in radar?
The echo method is sued to detect the presence of an obstacle and also to find its range
Which waves are used in radar?
Radio waves or microwaves
How does radar work?
A signal of electromagnetic waves is sent in space which after reflection from the object in the path, returns to the radar itself
What is the location of the transmitter and the receiver in RADAR and SONAR?
They are placed close to each other
In the medical field, what is the echo method of ultrasonic waves used for?
For imaging human organs (such as liver, gall bladder, uterus, womb) - called ultrasonography
Name the process of obtaining the image of the human heart by using ultrasonic waves
Echo cardiography
