Sound Flashcards
How is sound produced?
- Sound is produced by vibrating objects.
- The matter or substance through which sound is transmitted is called a medium.
- When an object vibrates, it sets the particles of the medium around it vibrating.
- A particle of the medium in contact with the vibrating object is first displaced from its equilibrium position and exerts a force on the adjacent particle which gets displaced from its position of rest.
- After displacing the adjacent particle the first particle comes back to its original position.
- This process continues in the medium till the sound reaches your ear
What is a wave?
- A wave is a disturbance that moves through a medium when the particles of the medium set neighbouring particles into motion and produce similar motions in others.
- The particles of the medium do not move forward themselves, but the disturbance is carried forward.
- Hence, sound is visualised in waves.
How does sound propagate?
- Air is the most common medium through which sound travels.
- When a vibrating object moves forward, it pushes and compresses the air in front of it creating a region of high pressure. This region is called compression (C).
- When the vibrating object moves backwards, it creates a region of low pressure called rarefaction (R).
- As the object moves back and forth rapidly, a series of compressions and rarefactions are created in the air which makes the sound wave propagates through the medium.
What is another way to visualise sound?
- Pressure is related to the number of particles of a medium in a given volume.
- More dense particles in the medium give more pressure and vice versa.
- Thus, the propagation of sound can be visualised as the propagation of density variations or pressure variations in the medium.
Does sound need a medium to propagate?
Sound is a mechanical wave and needs a material medium like air, water, steel etc. for its propagation.
Are sound waves longitudinal waves?
- In sound waves, the individual particles of the medium move in a direction parallel to the direction of propagation of the disturbance.
- The particles do not move from one place to another but they simply oscillate back and forth about their position of rest.
- This is how a sound wave propagates, so sound waves are longitudinal waves.
What are transverse waves?
- In a transverse wave, particles do not oscillate along the direction of wave propagation but oscillate up and down about their mean position as the wave travels.
- Thus, a transverse wave is one in which the individual particles of the medium move about their mean positions in a direction perpendicular to the direction of wave propagation.
List the Characteristics of Sound.
i. Amplitude
* The maximum displacement of particles in the medium from their original mean position, when a wave passes through the medium is the amplitude of a wave.
—
ii. Wavelength
* The distance between the centres of 2 consecutive compressions or rarefactions is equal to the wavelength.
* it is denoted by the greek letter λ (lambda)
—
iii. Time Period
* time taken by a particle to complete a full vibration is the time period for that part.
* si unit of time is second (s).
—
iv. Frequency
* it is no. of vibrations produced in one second. the si unit of frequency is Hertz (Hz).
* frequency = no. of vibrations/total time
* frequency = 1/t
* frequency is directly proportional to pitch.
—
v. Speed
* The distance travelled by the wave in one second is called its velocity.
* speed = wavelength*frequency
What are the laws of reflection?
- the incident ray, reflected ray and normal all lie on he same plane.
- angle of incidence = angle of reflection
What is an echo?
Echo is the repetition of sound caused by the reflection of sound waves.
What are the conditions necessary for an echo?
The two conditions necessary for an echo are:
1. the minimum distance between the sound source and the reflective surface should be at least 17.2 metres.
2. To hear a distant echo, the time interval between the original sound and echo must be 0.1 seconds.
Can you hear an echo when the distance between the sound source and the reflecting surface is less than 17.2 metres?
No, an echo can’t be heard if the distance between the sound source and the reflecting surface is less than 17.2 m because the time between hearing the original sound and the echo is less than 0.1 and humans can’t distinguish between successive sounds.
What is reverberation?
- Reverberation is the phenomenon of persistence of sound caused by multiple reflections of sound even after the source has stopped.
- When the time period between the original and reflected is less than 0.1 s reverberation occurs.
List the applications of multiple reflections.
- Megaphones/horns are designed to send sound in a particular direction without spreading it in all directions, a tube followed by a conical opening reflects sound successively guiding most of the sound waves from the source in the forward direction towards the audience.
- In stethoscopes the sound of the patient’s heartbeat reaches the doctor’s ears by multiple reflections of sound.
- The ceilings of concert halls and cinema halls are curved so that sound after reflection reaches all corners of the hall, the soundboard is placed behind the stage so that the sound, after reflecting from the soundboard, spreads evenly across the width of the hall.
What is the range of hearing of humans?
- The audible frequency for humans is from 20Hz to 20,000Hz.
- frequencies below 20Hz are called infrasound.
- frequencies above 20,000Hz are called ultrasound.
