WAVE MOTION & SOUND - 3

 Sound:
1) Sound is a form of energy which emitted by a vibrating body that travels in the form of wave and causes sensation of hearing
2) Sound  can't travel through vacuum
Production of sound:
Sound is produced when a body vibrates
Activity-1: 

1) Take a drum & beat it 
2) you will hear the sound of the Drum
3) now touch the membrane of the Drum
4) you will be able to feel it's vibrations
5) when the sound stops, touch the membrane of the Drum again
6) you will not feel any vibrations
7) so we can say that only vibrating membrane of the Drum produces the sound .
Activity-2: 

1) Take a metre scale 
2) place it on the table
3) press one end of the meter scale with your left hand
4) press the other end of scale in downward with your right hand and leave.
5) it causes vibrations in the scale & produces the sound
6) now stop the meter scale from vibrating
7) it will also stops producing sound 
Activity-3: 

 1) stretch a string by holding one end in your mouth under the teeth
2) hold the other end in one hand
3) pluck it near the middle you will notice that the string  starts vibrating.
4) vibrating string produces sound 

EXPERIMENT:

Aim: to demonstrate that sound produced by a vibrating body

Apparatus: 

                      1) Tuning fork 

                      2) Rubber Pad 

                      3) Table tennis ball

                      4) Thread 

                      5) Stand

Procedure :

1)  hit the tuning fork hard against rubber pad 

2) it produces sound

3) if you look at the prongs of the tuning fork closely, they look hazy because they are vibrating

4) suspend the table tennis bal with the thread tied to the stand

5) bring the prong of the vibrating tuning fork near the ball

6) the ball jumps to-and-fro 

7) this shows that the prongs of the tuning fork are vibrating. 

Result:

Every source of sound is a vibrating body 

EXPERIMENT-2: 

Aim:  to demonstrate that sound requires a medium for propagation

Apparatus:

                     1) Electric bell

                     2) glass bell jar

                     3) vacuum pump

                     4) Battery 

Procedure:

1) place the electric bell inside the glass bell jar and connect it to a battery

2) when the circuit is closed you can hear the bell ring

3) the jar contains air and sound travels through this air

4) remove the air from the jar with the help of the vacuum pump connected to the bell jar

5) as the air is taken out , the loudness of the sound slowly decreases

6) finally you can't hear the bell even though hammer of the bell is seen striking the gong as before the

7) Allow air in to enter the jar you will hear the sound slowly increasing

Result:

Sound cannot propagate in the absence of a material medium like solid, liquid or gas

Speed of sound in different media :

The speed of sound is more in solids less on liquids and least in gases. 

The speed of sound is nearly 5100 m/s in steel , 1450 m/s in water and 330 m/s in air at 0⁰ C

Mathematical formula For speed of sound :

1) 

2) Laplace's formula velocity of sound=

      

P ➞ Pressure of the medium 

⍴ ➞ Density  of the medium 

Factors effecting the speed of sound in a gas :

1) Density

2) Temperature

3) Humidity

4) Direction of wind

1) Effect of density :

Speed of the sound inversely proportional to the square root of the density.

The density of oxygen is 16 times the density of hydrogen therefore he speed of the sound in hydrogen is four times the speed of the sound in oxygen 

2) Effect of temperature: 

The speed of the sound increases with increase in temperature of gas 

The speed of sound in air increases by 0.6 m/s or 60 cm/s for each ⁰C

Example:

The speed of sound in dry still air at 0⁰C  is 330 m/s. At 25⁰ C, the speed of sound in dry still air will be?

3) Effect of humidity:

The presence of water vapour reduces the density of air.

Density of moist air  is less than density of dry air.

Velocity of sound in moist air greater than velocity of sound in dry air .

Since, 

Sound travels faster on a rainy day than on a dry day 

4) Effect of wind: 

If the wind blows in the same direction of in which the sound travels, the velocity of sound increases.

If the wind blows in the opposite direction in which the sound travels, the velocity of sound decreases.

Factors which do not effect the speed of sound in air :

1) Change in frequency 

2) Change in amplitude 

3) change in pressure 

4) change in factors like phase, loudness, pitch, quality of sound 

Effect of Pressure:

If pressure of the gases doubled the volume becomes half so density gets doubled and p/⍴ remains constant.

Comparison of speed of sound with speed of light.

The speed of light is 3