a) What do you notice? b) How do they produce sound?

Question

Sound has energy: 

(OR)

Suggest an activity to prove “sound has energy”.

Take a plastic bottle and a cell phone. Cut the top of the bottle so that it looks like a glass. Play songs on the mobile phone in high volume and place it in the bottle. Close the mouth of bottle with a balloon using rubber band so that it covers the bottle as shown in the figure and stretch it tightly so as to behave like a diaphragm. Place some sugar crystals or small size of sand particles on the balloon diaphragm and observe the movement of particles. Do the same activity after removing the phone from the bottle.

Sound has energy

a) What do you notice?

b) How do they produce sound?

c) Why there is a difference between the sounds produced by various musical instruments?

d) Which part of these instruments is responsible for production of sound?

e) Can you name the instrument for which more than one part is responsible for the production of sound?

f) How do you compare the production of sound in a flute and sound produced in a water tap when it is turned on, just before the water flows out of it.

Answer 1

a) When there is no cell phone inside the bottle, sand particles on diaphragm remain stationary. While the cell phone playing songs inside the bottle, the diaphragm vibrates which can be seen through dancing of sand particles. The sound produced by cell phone inside the bottle is responsible for these vibrations. Thus sound has energy to make sand particles vibrate on the diaphragm.

Musical instruments:

You might have observed many musical instruments like Tabala, Flute, Harmonium and Guitar. The sounds produced by these instruments are distinct. It is easy for us to identify which sound is coming from which instrument.

b) They produce sound due to vibration.

c) The mode of vibration is different.

d) Different parts for different instruments:

Name of instrument	Vibrating part of it
Tabala	Membrane, air inside hollow body
Veena	String fixed on hollow wooden board
Flute	Air columns
Clarinet	Air columns
Guitar	String fixed on hollow wooden board
Mridangam	Membrane, air inside hollow body

e) Tabala, Mridangam.

f) Both are same process. They produce sounds due to vibrating air columns.