Sounds Flashcards
What are mechanical waves?
When the medium particles vibrate, there is a change of kinetic energy into potential energy and vice versa. so sound waves are also called elastic or mechanical waves.
Define the following terms in relation to a wave — (a) amplitude, (b) frequency, (c) wavelength and (d) wave velocity.
(a) Amplitude (a) — When sound waves travel in a medium, the maximum displacement of the particle of medium on either side of its mean position, is called amplitude of the wave.
(b) Frequency (f) — The number of vibrations made by the particle of the medium in one second.
(c) Wavelength (λ) — The distance travelled by a wave in one time period of vibration of the particle of the medium, is called the wavelength.
(d) Wave velocity (V) — The distance travelled by the wave in one second.
A wave passes from one medium to another medium. Mention one property of the wave out of speed, frequency or wavelength (i) which changes, (ii) which does not change.
When a wave passes from one medium to another medium, thewavelength (or speed)of the wave changes.
(ii) When a wave passes from one medium to another medium, , thefrequencyof the wave does not change.
State two factors on which the speed of a wave travelling in a medium depends.
The two factors on which the speed of a wave travelling in a medium depends are —
(i) Elasticity and
(ii) Density
State two differences between the light and sound waves.
Light waves
These are the electromagnetic waves.
Sound waves
These are the mechanical waves.
Light waves
They can travel in a vacuum.
Sound waves
They require a material medium for propagation. They cannot travel in a vacuum.
What do you mean by reflection of sound?
The return of a sound wave on striking a surface such as a wall, metal sheet, plywood etc. back in the same medium is called reflection of the sound wave.
State one condition for the reflection of a sound wave.
The only requirement for the reflection of sound wave is that the size of the reflecting surface must be bigger than the wavelength of the sound wave.
Name a device in which reflection of a sound wave is used.
The phenomenon of reflection of sound wave is utilized in making the megaphone (or speaking tube).
What is meant by an echo?
The sound heard after reflection from a distant obstacle (such as a cliff, a hillside, the wall of a building, edge of a forest, etc.) after the original sound has ceased, is called an echo.
State two conditions necessary for an echo to be heard distinctly.
The two conditions for an echo to be heard distinctly are —
*The minimum distance between the source of sound (or observer) and the reflector in the air must be 17 m.
*The size of the reflector must be large enough as compared to the wavelength of the sound wave
State two applications of echo.
The applications of echo are —
*Dolphins detect their enemy and obstacle by emitting the ultrasonic waves and hearing their echo.
*In medical field, echo method of ultrasonic wave is used for imaging the human organs (such as liver, gall bladder, uterus, womb, etc.) This is called ultrasonography.
State the use of echo by a bat
Bats fly with speed much lower than the speed of sound. The sounds produced by the flying bats gets reflected back from an obstacle in front of it. By hearing the echo, the bats come to know, even in the dark, the location of the obstacle, so they turn from their path and fly safely without colliding with it. This process of detecting obstacle is called sound ranging.
State the use of echo by a dolphin
Dolphins detect their enemy and obstacle by emitting the ultrasonic waves and hearing their echo. They use ultrasonic waves for hunting their prey.
State the use of echo by a fisherman.
A fisherman sends an ultrasonic pulse (a very high frequency vibrator) from a source and receives the pulse reflected from the shoal of fish in a detector. Hence, afisherman use echoes to catch fishes.
How do bats avoid obstacles in their way, when in flight?
Bats fly with speed much lower than the speed of sound. The sounds produced by the flying bats gets reflected back from an obstacle in front of it. By hearing the echo, the bats come to know, even in the dark, the location of the obstacle, so they turn from their path and fly safely without colliding with it. This process of detecting obstacle is called sound ranging.
Bats can produce and detect the sound of very high frequency up to about 100 kHz.
What is meant by sound ranging?
Sound ranging is the process of detecting obstacles with the help of echo.
Give one use of sound ranging.
Animals like bats, dolphin use sound ranging to detect their enemies.
Name the waves used for sound ranging.
Ultrasonic waves are used for sound ranging.
State one reason for sound ranging use.
Ultrasonic waves can travel undeviated through a long distance and so they are used for sound ranging.
Why are the waves mentioned by you not audible to us?
The range of audible sound waves is 20 Hz to 20,000 Hz, whereas ultrasonic waves have a frequency more than 20,000 Hz. Hence, ultrasonic waves are not audible to humans.
What is ‘SONAR’?
The word ‘SONAR’ stands for Sound navigation and ranging.
State the principle on which SONAR is based.
ultrasonic waves are sent in sea water in all directions, from the ship. These waves are received after reflection from an obstacle such as the enemy submarine, iceberg, sunken ship etc. Hence, the distance between the ship and the obstacle can be determined.
State the use of echo in medical field.
In medical field, echo method of ultrasonic wave is used for imaging the human organs (such as liver, gall bladder, uterus, womb, etc.) This is called ultrasonography.
The minimum distance between the source and the reflector in air, to hear an echo, is approximately —
17m
To detect the obstacles in their path, bats produce —
Ultrasonic waves
What do you understand by the natural vibrations of a body? Give one example.
The periodic vibrations of a body in the absence of any external force on it, are called the natural (or free) vibrations.
For example —
A body clamped at one point when disturbed slightly from its rest position, starts vibrating. The vibrations so produced are called the natural or free vibrations of the body.
What is meant by the natural frequency of vibrations of a body?
The natural frequency is the frequency at which a body tends to oscillate in the absence of any driving or damping force.
Name one factor on which natural frequence depends?
The natural frequency of vibrations of a body depends on the shape and size (or structure) of the body.
Where can a body execute the natural vibrations?
The natural vibrations can occur only in vacuum.
However, in practice it is very difficult to have vacuum. Hence, it is very difficult to realise such vibrations in real life
