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How does sound travel in air ?
Sound travels in air in the form of longitudinal waves...
What is audible sound?
Frequency between 20 Hz to 20,000 Hz is audible sound.
What is the unit of loudness?
Decibel (dB)
What are infrasonic sounds?
Sounds which have frequency lower than 20 Hz are called infrasonic sounds.
What is noise pollution?
The presence of unwanted and excessive sound in the environment is called noise pollution.
What is the relationship between time period and frequency???
Frequency = 1/Time period
Time period = 1/Frequency
Two astronauts are floating close to each other in space. Can they talk to each other without using any special device? Give reasons.
No, because in space there is no atmosphere and sound needs medium to travel.
What is the property of vibration which determines the pitch of the sound?
The frequency is the property which determines the shrillness or pitch of a sound. If the frequency of a sound is higher then we say that the sound has lower pitch.
Suppose a bell is ringing in a vacuum. Will you able to hear the sound?
We will not be able to hear the sound of vibration because sound cannot travel in vacuum.
What do you mean by oscillatory motion?
The to and fro motion of an object is called vibration. This motion in both the direction from its mean position is called oscillatory motion.
Define the following:
a) Amplitude
b) Time period
c) Frequency
a) Amplitude: The maximum displacement of a particle of medium on either side of its mean position
b) Time period: The time taken by a particle of medium to complete its one vibration
c) Frequency: The number of vibrations produced by a particle of the medium in one second
How is sound produced and how is it transmitted and heard by us?
Sound is a form of energy produced and transmitted by a vibrating matter. It travels in form of waves through matter and moves in to and fro direction. When this wave reach eardrum it makes the eardrum to vibrate. The eardrum sends vibrations to the inner ear. From there, the signal goes to the brain and we are able to hear the sound.
A string musical instrument was first plucked with a force of smaller magnitude and then with a force of greater magnitude. In which case would the instrument produce a louder sound?
The loudness of sound depends upon the amplitude of vibration. The amplitude of string is larger when it is plucked with greater force and hence the sound will be louder in that case.
Suppose a bell is ringing in a vacuum. Will you able to hear the sound?
We will not be able to hear the sound of vibration because sound cannot travel in vacuum.
If the loudness is doubled what would be the amplitude
amplitude = a^4
Why do we hear echos?
We hear echos when sound reflects off a hard surface and bounces back to our ears.
Out of a man and a woman:
(a) who has shorter vocal cords?
(b) who produces sound of higher pitch?
(a) Woman has short vocal chords. The male vocal chords are between 17 mm and 25 mm in length whereas of a woman are between 12.5 mm and 17.5 mm long.
(b) Woman produces sound of higher pitch.
Name one solid, one liquid and one gas through which sound can travel.
Solid: Iron
Liquid: Water
Gas: Air
State one observation from everyday life which shows that sound travels much more slower than light.
In case of thunder, we see the lightening first and then the sound of thunder. This is because, the velocity of light in air is while the velocity of sound in air is 343 m/s.
Name any two common musical instruments and identify their vibrating parts.
Dholak Diaphragm (stretched membrane)
Sitar Strings of the Sitar
Flute Air column inside the flute
State the differences between ultra sound and infra sound?
Ultrasonic sound
(i) Sound of frequency higher than 20,000 Hz is called ultrasonic sound.
(ii) Animals like dog, bat, monkey, deer, etc., can hear ultrasonic sound.
Infrasonic sound
(i) Sound of frequency lower than 20 Hz is called the infrasonic sound.
(ii) Animals like whale, elephant, hippopotamus, giraffe, etc., can hear infrasonic sound.
If you want to hear a train approaching from far away, why is it more convenient to put the ear to the track?
It is more convenient to put the ear to the track, If you want to hear a train approaching from far away because we can hear the vibrations from the ground when we put our ear at the track.
A pendulum oscillates 40 times in 4 seconds. Calculate its
(i) time-period, and
(ii) frequency.
Can we hear the sound produced by the oscillations of this pendulum? Give reason for your answer.
Frequency = 40 vibration/ 4 seconds = 10 Hz
Thus, time period = 1/f = 1/10 = 0.1 seconds.
No, we cannot hear because the audible human range is from 20Hz to 20,000 Hz.
What is the difference between noise and music? Can music become noise sometimes?
The Unwanted sound that is unpleasant to ear is called noise. A pleasant sound is called music.
Music can become noise in many instances. Music is of many types and everybody may not like each type of music. When someone listens very loud music, it can be noise for someone else.
What are the factors affecting the loudness of a sound? (4 points)
a) amplitude of the wave
b) distance of source of sound
c) surfacearea of the vibrating body
d) sensitivity of the listener