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Sound Needs a Medium for Propagation

  • Last Updated : 02 Jun, 2021

Without sound life is a little tough, isn’t it? Like imagine watching a horror movie without sound you will realize that the scary movie becomes a funny video compilation. We are totally connected to sound, from morning to our bedtime we hear several sounds some sounds good but at the same time, some sounds are bad. Sound not only help us to understand our surrounding, but it also helps us to communicate efficiently. In today’s world, we still value live interaction or voice calls rather than chats and emails. 

Humans take this sound for granted. Do you know astronauts can’t directly talk to each other in space! Have you ever wonder why they can’t? Well, we are going to answer this question in this article.

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What is Sound?

A sound is a form of energy, which produces a sense of hearing in our ears. The sound produces because of the vibration of any objects. You can take an example, in human beings the sound produces when there is vibration in vocal cords. Vibration basically the to and fro movement of the particles of an elastic body.



Or in other words, the sound is a type of energy that is created by the vibrating of particles in a medium. Let us look at an example to see how sound waves are created: When drumsticks strike a drum, the outside membrane of the drum vibrates up and down. The air close above the drum membrane is compressed whenever the drum membrane travels higher. Sound waves are related to everything around us. The chirping of birds, the drilling of machines, the buzzing of alarm clocks, the playing of the guitar, the bouncing of the ball, and so on all make a sound. But have you ever considered how we hear these sounds? So, what exactly is sound?

Just like water, sound also needs a medium, let’s discuss it in detail.

Sound needs a Medium

As we have discussed earlier, the vibration of an object causes sound, also sounds need medium. Medium is a matter through which sounds is propagated, it can be liquid, gas or solid. Let’s understand this by understanding a simple example. Suppose you want to travel in space, you can’t go without a rocket, here a rocket is your medium through which you can travel to space, likewise sound also needs a medium to propagate from one place to another. The molecules of the matter carry sound waves, so without any medium sound can’t propagate.

This is the reason why astronauts cannot talk with each other directly in space as there is a vacuum in space, hence there is no molecule present that can carry the sound waves. 

Because the molecules of solids, liquids, and gases convey sound waves from one point to another, sound requires a material medium such as solid, liquid, or gas to move. Because there are no molecules in the vacuum that can vibrate and convey sound waves, sound cannot travel through it.

Experiment

Let’s do an experiment to understand the above statement.

Bell Jar Experiment to show sounds need a medium

Material Required:

  • An airtight bell Jar
  • Vacuum Pump
  • Electric Bell

Procedure:



  • Take an airtight glass bell jar, so that air cannot leak during the experiment.
  • Suspend the electric bell inside the bell jar, and switch on the electric connection, now listen to the sound of the bell.
  • Start the connected vacuum pump of the bell jar, meanwhile, you will notice the sound of the bell is no longer audible as before. Gradually when all the air gets the pump out from the jar you will notice you are not able to hear a sound. The current is the same but still, you can’t able to hear the sound.

This means that still the sound is being produced but now we cannot hear it. This is because sound waves always need a medium to propagate. In the bell jar, it was, hence sound waves cannot travel.

Hence, the experiments prove to us that sounds need a medium to propagate.

Sample Problems

Problem 1: Suppose there is an explosion in space, so now are you able to hear the sound? If yes why? if not why not?

Solution:

 No, since in space vacuum is present, so there is no molecule present that can carry the sound waves. Thus, we cannot be able to hear the sound of an explosion.

Problem 2: Write an experiment to illustrate sounds that need a medium for propagation.

Solution:

We can illustrate this through the bell jar experiment.

  • Take an airtight glass bell jar, so that air cannot leak during the experiment.
  • Suspend the electric bell inside the bell jar, and switch on the electric connection, now, listen to the sound of the bell.
  • Afterwards, start the connected vacuum pump of the bell jar, meanwhile, you will notice the sound of the bell is no longer audible as before. 
  • Gradually when all the air gets the pump out from the jar you will notice you are not able to hear a sound. The current is the same but still, you can’t able to hear the sound.
  • The above experiments prove that sounds need a medium to propagate.

Problem 3: In which medium sounds propagates fastest and give a reason for this?

Solution:

Speed of sound depends on density, more is the density more fast sound will propagate, because in denser medium molecules are closely packed, so it helps sound to travel faster. Therefore, in solid the sound will propagate fastest.

Problem 4: Explain why two astronauts can’t able to talk on the moon directly?



Solution:

Astronauts can’t able to talk in space due to the presence of vacuum in space thus without medium sound cannot be able to travel and it requires a radio transmitter to exchange message.

Problem 5: What is medium, and what are the different types of medium?

Solution:

Medium is a matter through which sounds is propagated, it can be liquid, gas or solid.

Problem 6: Why sound cannot be able to propagate in a vacuum?

Solution:

Since sounds need a medium, in a vacuum there is no molecule present that can carry the sound waves and sound cannot able to propagate.

Problem 7: Suppose an electric bell is suspended inside the bell jar, but there is leakage of air, now tell me when you supply electricity to the electric bell, will you be able to hear the sound of the bell. Give reason.

Solution:

Yes, we can, as there is leakage in the glass jar due to which the desirable vacuum will not be maintain, thus we will able to hear the sound of the bell.

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