Propagation of Sound Q/A
1. Answer the following
(a) Give a simple
experiment to show that a medium is necessary for the propagation of sound.
(b) How is sound produced
in drums?
(c) What is a noise?
2. Give reasons:
(a) A table player
tightens or loosens the bands tying down the membrane.
(b) We hear thunder long
after we have seen the flash of lightning.
(c) A surface is necessary
for an echo to be heard.
3. Match the column
Group
‘A’ Group ‘B’
(a) Reflection of sound 1. The pegs on the sitar.
(b) Pollution of sound 2. Water
(c) Medium of sound 3. Echo point
(d) Frequency of sound 4. Noise
4. Fill in the blanks
(a) A flautist can place figures
on the proper holes and produce vibrations of the …………
(b) Sound is heard more
clearly …………… as compared to air.
(c) In drums, ……………..
vibrates to produce sound.
(d) The speed of light is ……………………
times that of the sound.
(e) When temperature
increases the speed of sound ……………….
1. Answer the following
(a) Give a simple
experiment to show that a medium is necessary for the propagation of sound.
Ans: Aim –
To verify that a medium is necessary for the propagation of sound.
Requirements – 1) Take a round bottomed flask with some water in
it and close it with a two holed rubber stopper. 2) Take a two holed rubber
stopper and pass a glass rod or wire through one hole. 3)Tie a bell to one end
of the rod and fit the stopper to the flask. 4) Pass a glass tube through
another hole and attach a piece of rubber tubing fitted with a clamp to close
it.
Experiment
– 1) Open the clamp and heat the
flask till water boils and steam comes out through the rubber tube. 2) Stop
heating the flask and clamp the rubber tube shut. 3) Allow the flask to cool.
Observation
– 1) The steam inside cools and condenses.
2) We cannot hear the ringing of the bell because after steam condenses, there is
no medium left inside to carry the sound out of the flask. 3) When we open the
clamp and allow outside air to enter inside, that air acts as medium and hence we
hear the sound of the bell.
Figure
– 
Conclusion
– The medium is necessary for the
propagation of sound.
(b) How is sound
produced in drums?
Ans:
1) A drum is a percussion instrument having a stretched membrane
tied very tightly over it.
2) The tension in the membrane can be varied.
3)
When the membrane is struck, the tensed membrane starts vibrating which results
in sound.
4)
The desired frequency can be obtained by adjusting the tension in the membrane.
(c) What is a noise?
Ans:
1)
Noise is an unwanted sound
2)
Noise follows no rules; frequencies change constantly, loudness changes
irregularly.
3) Nothing can be understood if there is noise.
4) Noise pollution is a social problem.
Example : Noise of traffic.
2. Give reasons:
(a) A tabla player
tightens or loosens the bands tying down the membrane.
Ans:
1)
A tabla is a percussion instrument having a stretched membrane tied very
tightly over it.
2) The tension in the membrane can be varied.
3)
When the membrane is struck, the tensed membrane starts vibrating which results
in sound.
4)
The desired frequency can be obtained by adjusting the tension in the membrane.
5)
Hence a tabla player tightens the bands tying down the membrane.
(b) We hear thunder
long after we have seen the flash of lightning.
Ans:
1)
The speed of sound in air is about 340 metres per second (340 m/s)
2) Light travels at about 3 x 108 m/sec.
3)
That is, light travels at a speed which is about 106 times,
or a million times, that of sound.
4)
Therefore, though thunder and lightning occur at the same time, the flash of
lighting travels faster than sound of thunder.
5)
Hence we hear thunder long after we have seen the flash of lightning.
(c) A surface is
necessary for an echo to be heard.
Ans:
1)
For an echo to be heard, the sound should be reflected back from some surface.
2)
In an echo, the sound is reflected from a flat surface and travels back in the
direction from which it came.
3)
At echo points the echo is heard only after the sound is reflected from some
opposite mountains.
4)
Therefore a surface is necessary for an echo to be heard.
3. Match the column
Group
‘A’ Group ‘B’
(a) Reflection of sound 3. Echo point
(b) Pollution of sound 4. Noise
(c) Medium of sound 2. Water
(d) Frequency of sound 1. The pegs on the sitar.
4. Fill in the blanks
(a) A flautist can place figures
on the proper holes and produce vibrations of the air column.
(b) Sound is heard more
clearly through water as compared to air.
(c) In drums, membrane vibrates to produce sound.
(d) The speed of light is 106 or a million times that of the sound.
(e) When temperature
increases the speed of sound increases.
