What is sound?
Ans: Sound is a form of energy produced due to the vibration of an object.
The sound absorbing materials are used in the walls of the auditoriums. Why?
Ans: The sound absorbing materials are used in the walls of the auditoriums to minimize reverberation.
What is amplitude?
Ans: The maximum displacement of a vibrating body from its mean position is called amplitude.
What is echo?
Ans: The repetition of sound caused due to its reflection is called echo.
What is frequency?
Ans: The number of complete vibrations made by a particle of a body in one second is called frequency.
What is wavelength?
Ans: The distance between two successive compression or rarefaction is called wavelength.
What is infrasonic sound?
Ans: The sound with frequency less than 20 Hz is called infrasonic sound.
What is ultrasound?
Ans: The sound with frequency greater than 20 kHz is called ultrasound.
What is time period?
Ans: The time taken by a vibrating body to complete one vibration is called time period.
What is an audible sound?
Ans: The sound with frequency between 20 Hz to 20 kHz is called audible sound.
What is transmission of sound?
Ans: The phenomenon due to which the sound travels from one place to another is called transmission of sound.
The sound of thunder is heard later than the flash of lightning. Why?
Ans: The sound of thunder is heard later than the flash of lightning because the speed of sound is very less than the speed of light.
What is frequency? What do you mean by frequency of sound is 50 Hz?
Ans: Frequency is defined as the number of complete vibrations made by the vibrating particles in one medium.
Frequency of sound is 50 Hz; it means that 50 complete sound waves are being produced in 1 second.
Write any two differences between echo and reverberation.
Ans: The differences between reverberation and echo are as followings:
Reverberation EchoReverberation is defined as prolongation of sound produced by a series of reflection.The repetition of sound caused due to its reflection is called an echo.The minimum distance between the source of sound and the reflecting body should be 17 m.The distance between the source of sound and the reflecting body should be less than 17 m.
What is sound? Write unit of frequency and wavelength.
Ans: Sound is one type of energy which is possessed due to vibration of bodies and can be experienced by our ears.
The unitsof frequency and wavelength are Hz and metre respectively.
What is wavelength? Calculate the velocity of sound having frequency 100Hz and wavelength 3.3m.
Ans: The distance between two consecutive compressions or refractions of a sound wave is called wavelength of that wave.
Here,
Given,
Frequency (f) = 100 Hz
Wavelength (ʎ) = 3.3 m
Velocity (V) =?
We have,
V = f х ʎ = 100 х 3.3 = 330 m/s
Hence, the velocity of sound wave is 330 m/s.
What is transverse wave? Write one effect of reverberation.
Ans: If the particles medium vibrate perpendicular to the direction of the motion of the wave, such a wave is called transverse wave.
Due to effect of reverberation, original sound gets reflected and reflected sound mixes with original sound and prolongation of sound occurs.
Astronauts wear special device on their ear, why? Define wavelength.
Ans: Sound wave is mechanical wave i.e. it need a material medium to for their propagation. In space there is vacuum i.e. no air is present for the propagation of sound, so astronauts cannot communicate with each other. Hence, astronauts wear special device on their ear for communication.
The distance between two consecutive compressions or rarefactions of a sound wave is called wavelength of that wave. It is denoted by 'ʎ'.
What do you mean by sources of sound? Give some examples.
Ans: The objects which vibrate continuously or the objects that we make vibrate are called the sources of sound.
For example: Guitar, Madal, Radio, Whistle etc.
Sound is not heard on the surface of the moon. Why?
Ans: Sounds are mechanical waves i.e. they need material medium to travel. The earth has atmosphere consisting air which acts as the medium of sound. But it is vacuum on the surface of moon i.e. there is no material medium. Hence, sound cannot be heard on the surface of the moon.
Why is sound called a longitudinal wave?
Ans: Sound wave is called a longitudinal wave because the particles of the medium vibrate in the direction of the propagation of the wave.
What is a wave?
Ans: A wave is a disturbance that travels in a medium due to repeated periodic motion of particle about their mean position, - such that the disturbance is handed over from one particle to the other without the actual motion of the medium.
What is oscillation, time period, frequency and vibration?
Ans: Each complete movement of an oscillating body is called an oscillation.
Time taken to complete one oscillation is called time period.
The number of complete oscillation made in one second is called frequency.
The up and down or to and fro movement of a body is called vibration.
What is compression and rarefraction?
Ans: A compression is a region in a longitudinal wave where the particles are closest together.
A rarefaction is a region in a longitudinal wave where the particles are furthest apart.
What is the audible range of human ear? Write the range of Infrasonic and Ultrasonic sound.
Ans: The audible range of human ear is 20 Hz to 20,000 Hz.
i. Infrasonic Sound: 1 Hz to 20 Hz
ii. Ultrasonic Sound: Above 20,000 Hz
Explain sound.
Ans: Sound is a form of energy which produces sensation of hearing to our ears. It is a mechanical wave because it needs material medium to travel. Human ears cannot hear every sound that is produced because the range of human ear is 20 Hz to 20,000 Hz. The sound lower than this frequency is known as infrasonic sound and the sound above this range of frequency is known as ultrasound.
Describe an experiment to show that sound can travel in solids.
Ans: Go to near a table with your friend. Tell your friend to stand on the other side of the table. Keep your one ear pressed gently on the surface of the table and close the other ear with your finger. Tell your friend to gently knock at the other edge of the table. You will hear the sound clearly. This experiment describes the ability of sound to travel in solid medium.
Describe hearing process in brief.
Ans: The hearing process mainly includes these three steps:
i. Source of sound: A vibrating body produces sound. Thus, the source of sound is a vibrating body.
ii. Medium for propagation of sound: As sound is a mechanical wave it needs material medium to travel. It can travel through all the states of matter namely: solid, liquid and gas.
iii. Sound receiver: Our ear acts as a sound receiver. When the sound hits the diaphragm of ear, it starts to vibrate. The vibration is further processed by brain to give a clear sense of sound.
Write short notes on propagation of sound in different medium.
Ans: Sound is a mechanical wave and it needs material medium to propagate. The sound wave can travel through all the states of matter i.e. solid, liquid and gas. But the velocity of sound is not equal in the entire medium. The velocity of the sound is maximum in the solid medium and least in the gaseous medium. In solids sound propagate in the form of transverse wave and in liquid and gas it travels in the form of longitudinal wave.
Describe three examples which show that sound is produced due to vibration.
Ans: We have seen people playing guitar. In guitar when they pluck the strings of guitar, it vibrates and produces sound. Sound produced by it travels through air which acts as the medium.
Another example is a tuning fork. Fork consists of two tines and a handle. When the fork is struck on hard surface the two tines starts vibrating. The back and forth motion of tines produces disturbances in the surrounding air molecules resulting sound to be heard.
The sound produced by us is also the result of vibration. When we speak the vocal chords vibrate which comes out from our mouth and travel through air.
The frequency of an oscillating body is 10 Hz. Calculate the total oscillations made in 50 second.
Ans: Given,
Frequency (f) = 10 Hz
Time period (T) =?
Total oscillation in 50 second =?
We know time and frequency are related by the relation:
Frequency = 1/(Time Period)
or, 10 = 1/(Time Period)
∴ Time Period = 1/10 = 0.1 s
Now,
In 0.1 s the body oscillates 1 time.
In 1 s the oscillation made by the body = 1/0.1 = 10
In 50 s the total oscillations made by the body = 10 ⨉ 50 = 500 oscillations.
Therefore,
Time period = 0.1 s and the total oscillations made in 50 seconds = 500
A stone takes 2 seconds to complete 10 oscillations. Calculate the time period of oscillation and frequency.
Solution: For 10 oscillations, time = 2s
For 1 oscillation, time = 2/10s
∴ Time period of oscillation 0 0.2s
Also,
Frequency is calculated as:
In 2 second, the stone completes 10 oscillations
In 1 second, the stone completes 10/2 = 5 oscillations.
∴ Frequency = 5 oscillations per second.
Alternatively,
Frequency = 1/(Time Period)
= 1/0.2
= 5 oscillation per second or 5 Hz.
Differentiate between music and noise.
Ans: The differences between noise and music are as follows:
Music
Noise
1. It is produced by periodic vibrations.
1. It is produced by irregular vibrations.
2. It has regular wave pattern.
2. It has irregular wave pattern.
3. They are pleasing to our ears.
3. They are unpleasant to our ears.
4. As they are periodic waves they can be reproduced.
4. They are non-periodic wave so they cannot be reproduced.
Example: Sound produced by musical instruments like guitar, drum etc.
Example: Sound produced by moving bus, train, mixer grinder etc.
Differentiate between transverse and longitudinal wave.
Ans: The differences between transverse and longitudinal waves are as follows:
Transverse Wave
Longitudinal wave
1. In transverse waves, the particles of the medium vibrate perpendicular to the direction of wave.
1. In longitudinal waves, the particles of the medium vibrate along the direction of wave motion.
2. These waves travel in the form of alternate crest and troughs.
2. These waves travel in the form of alternate compressions and refractions.
3. These waves can be transmitted through solids or over liquids.
3. These waves can be transmitted through all the three type of media i.e. solid, liquid and gas.
Examples:
i) Ripples formed over water surface.
ii) Waves produced in stretched strings.
Examples:
i. Sound waves in air.
ii) Waves formed along a compressed spring.
What is wave motion? Define different types of wave.
Ans: Wave motion is a form of disturbance which travels through the medium due to particles of the medium about their mean position.
There are two types of wave:
• Transverse wave: The wave where the particles of the medium vibrate perpendicular to the direction of wave is known as transverse wave. The maximum positive displacement is known as crest and the maximum negative displacement is known as trough.
• Longitudinal wave: The wave where the particles of the medium vibrate along the direction of wave motion is known as longitudinal waves. In this type of wave, particles move to and fro to the direction of the wave giving rise to compressions and refractions.
What is crest and trough?
Ans: The maximum displacement in the positive direction produced by transverse wave is known as crest.
Trough is a depression i.e. maximum displacement in the negative direction.
Name the medium A, B and C according to the speed of sound.MediumVelocity of soundA5130 m/sB1500 m/sC344 m/s
Ans: In the above table the mediums of sound are:
A - Iron
B - Water
C - Air
Describe three examples which show that sound is produced due to vibration.
Ans: We have seen people playing guitar. In guitar when they pluck the strings of guitar, it vibrates and produces sound. Sound produced by it travels through air which acts as the medium.
Another example is a tuning fork. Fork consists of two tines and a handle. When the fork is struck on hard surface the two tines starts vibrating. The back and forth motion of tines produces disturbances in the surrounding air molecules resulting sound to be heard.
The sound produced by us is also the result of vibration. When we speak the vocal chords vibrate which comes out from our mouth and travel through air.
Write short notes on propagation of sound in different medium.
Ans: Sound is a mechanical wave and it needs material medium to propagate. The sound wave can travel through all the states of matter i.e. solid, liquid and gas. But the velocity of sound is not equal in the entire medium. The velocity of the sound is maximum in the solid medium and least in the gaseous medium. In solids sound propagate in the form of transverse wave and in liquid and gas it travels in the form of longitudinal wave.