SOUND : EASY WAY TO EXPLAIN VIBRATION
We use to listen many noises around us every day in our daily life. In case of doorbell the note produces by vibration of bell. Sound plays an important role in our lives and helps us to communicate with others. Various musical instruments produces different musical notes from flute, sitar, table, harmonium.
SOUND PRODUCED BY A VIBRATING BODY
Vibration is the to and fro back and forth motion of an object. If we pluck a tightly tied stretched band , then it vibrates and produces sounds. If it stops vibrating, then it does not produce sound. Some times when we pluck the string of an instruments like sitar then the note which we hear is not only that of string. The whole instruments is ready to vibrate to produce the sounds of sitar. There are some other types of musical instruments like manjira, ghatam, the mudpots and kartal which we mainly use in folk songs and dances. Similarly, when we beat mridangam’s the skinny membrane then note comes from whole part of insrtument.
TERMS RELATED TO SOUND
AMPLITUDE (a) : Maximum displacement of a vibrating object from its central position is amplitude. It makes the sound louder. More amplitude is the character louder voice.
TIME PERIOD (T) : Time taken by a vibrating or oscillating object to complete one vibration is time period. SI unit of measuring time period is second.
FREQUENCY (f): Number of oscillation per second represents frequency. Measuring unit is hertz (Hz). If an object makes one vibration in one second the its frequency is 1hz.
CHARACTERISTICS OF SOUND
LOUDNESS: It depends on the amplitude of vibrations of vibrating body. If we pluck the sitar string lightly, then it vibrates with small amplitude and produces very faint noise. On the other hand, when we pluck the string hard, then it starts vibrating with large amplitude and produces a loud noise. Loudness of depends on the amplitude of vibration of sound producing objects. Loudness is proportional to the square of the vibration producing the sound. If the amplitude is double then the loudness will be four times more.. We term the unit of loudness as decibel (db).
PITCH: We can differentiate various sounds of same loudness with the help of pitch of sound. We can distinguish male voice from female voice on the basis of their shrillness. Pitch of sound depends on the frequency of vibration of sound producing object. If the frequency is higher, the sound is shrill. This sound has higher pitch. Lower frequency produces lower pitched sound. Drum vibrates with a low frequency. Roar of lion is very loud but the sound of the bird is quite feeble. Voice of woman has a higher frequency. It is shriller than that of a man.
QUALITY: By this character we can recognize different sounds with the help of loudness and pitch. Song sang by different singers we can recognize by this quality.
AUDIBLE AND INAUDIBLE SOUNDS
Sounds of frequencies less than about 20 vibrations per second (20 Hz) if produced, we cannot hear the voice. This sound we term as inaudible. On the other hand, sounds of frequencies higher than 20,000 vibrations per second (20 kHz) if produced, that noise also we cannot hear. This is also inaudible. The sounds of frequencies lesser than 20Hz are infrasonics. The sounds of frequencies greater than 20,000 Hz are ultrasonics. Bat can produce as well as hear ultrasonic. Dog also can hear the ultrasonic. Dog trainer police use whistles of high frequency which is audible to dog only.
SHORT TYPE QUESTION
Qs1: What is the frequency of wave with time period 0.025s?
Ans1: T = 0.025s
V = 1/T
= 1/0.025 = 40 Hz.
Qs2: What is the lowest limit of audible frequency?
Ans2: The lowest limit of audible frequency is 20 Hz.
Qs3: A baby recognizes her mother by her voice. Name the characteristics of sound involved.
Ans3: Pitch is that characteristic of sounds due to which baby can distinct his mother’s voice.
Qs4: How can you differentiate pitch from frequency?
Ans4: Pitch is perceptual to sensation. Frequency is a physical quantity that we can measure.
HIGHER ORDER THINKING SKILL
Qs5: Two astronauts are floating close to each other in space. How can they talk to each other? Is there any trick or device?explain
Ans5: No, they cannot talk to each other without using any special device because there is no medium in space and sound needs medium to travel. They use to talk in sign language.
Qs6: If a person eye is tied with a cloth, then how can he understand the presence of other players?
Ans6: The vibration due to the movement of closer player is more than others and the blind folded person easily imagine to which direction a player is nearer to her.
EXPLAIN THE ANSWER
Qs7: How sound travels slower than light, explain with example.
Ans7: We know that sound travels in air with 340 m/s velocity, whereas light travels in any medium or vacuum in 3 X 108 m/s speed. We can understand that sound travels slower than that of light. Light takes negligible time to reach few kilometers distance where sound takes few second to cross that same distance.
During thunderstorm, we use to observe flash of lightning first. Thunder sound reaches our ear few seconds after. Though both are produced in same time.
That is why people say, if you hear the sound of thunder after flash of lightning then think that you are safe.
ANSWER IN BRIEF
Qs8: How the sound transmits and reaches to our ear?
Ans8: When any object vibrates then sound is produced. These vibrations travel from the source through some particles of medium (air/solid/or water) in the environment. In this wat it reaches in the ear. Now, vibration enters into our ear by reflection of ear pinna. Then it travels through ear canal and reaches to ear drum. This fine membrane vibrates accordingly to send the vibration in the middle ear. Middle ear has three fine bones (malleus, incus, stapes). These bones amplify the vibration and sent to inner ear. Internal ear contain hearing receptor organ of corti which helps to hear the sound. By auditory nerve we can recognize the voice also.