Question 1

Describe an activity to show that sound requires a material medium for its propagation.

Accepted Answer

Sound is a mechanical wave that needs a material medium like air, water, steel, etc., for its propagation. A sound wave travels in the form of a longitudinal wave and it requires a material medium for its propagation.  Sound always originates from some vibrating body. These vibrations are produced by tuning forks, drums, bells, the strings of a guitar, etc. The bell jar experiment is a common experiment used to demonstrate that sound needs a medium to travel. A bell jar is a laboratory equipment used for creating a vacuum. It is so named as its shape is similar to that of a bell. A bell jar is placed on a base which is vented to a hose fitting that can be connected via a hose to a vacuum pump. By pumping the air out of the bell jar, the air pressure inside the jar can be varied. The experiment is done by placing an electrical bell in the bell jar. As the air is pumped out of the sealed bell jar, the sound from the bell jar fades. At a particular vacuum, no more sound is heard from the bell, but we can see that the hammer continues hitting the gong and sound is produced. However, the sound is not audible to our ears because of the vacuum inside the jar. This demonstrates that the sound wave cannot travel through vacuum. That is, a sound wave needs a material medium for its propagation.

Question 2

Choose the correct answer.Sound can travel through

Accepted Answer

Answer is D.Sound is a form of energy produced and transmitted by vibrating matter. Sound travels in waves. When sound moves through matter (solid, liquid, or a gas), the molecules of the matter move backward and forward in the direction in which the wave is traveling. This movement is called a vibration. Sound travels more quickly through solids than through liquids and gases because the molecules of a solid are closer together. Sound travels the lowest through gases because the molecules of a gas are farthest apart. In a vacuum sound cannot travel because there is no matter for it to move through.Hence, sounds can travel in solids, liquids and gases.

Question 3

Sound waves cannot travel through

Accepted Answer

Answer is D.Sound waves need to travel through a medium such as a solid, liquid, or gas. The sound waves move through each of these mediums by vibrating the molecules in the matter. The molecules in solids are packed very tightly. Liquids are not packed as tightly as solids. And gases are very loosely packed. The spacing of the molecules enables sound to travel much faster through a solid than a gas. Sound travels about four times faster and farther in water than it does in air. Sound waves are travelling vibrations of particles in media such as air, water or metal. So it stands to reason that they cannot travel through empty space, where there are no atoms or molecules to vibrate.Hence, Sound cannot travel through vacuum, but it requires a medium.

Question 4

Make a diagram of electric bell and explain its working system.

Accepted Answer

The electric bell: Figure shows a simple electric bell. It consists of an electromagnet, an armature, a contact adjusting screw, A gong and hammer. The armature consists of a soft iron rod mounted on a spring. One end of the iron rod presses against the top of the contact adjusting screen.When the switch is pressed on, current flows in the electromagnet. It then attracts the iron rod towards itself, causing the hammer to strike the gong. At the same time, the armature loses contact with the screw and the current is switched off. This causes the electromagnet to lose its magnetism and the armature springs back to its original position to close the circuit once again. Current flows again and the cycle repeats itself till the current is switched off.

Question 5

Two astronauts on the surface of the moon cannot talk to each other. Why

Accepted Answer

There is no atmosphere on the surface of the moon. Since there is no medium in between, the sound cannot travel from one astronaut to the another astronaut on the surface of the moon.

Question 6

An alarm bell is kept inside a vessel as shown in Figure. A person standing close to it can distinctly hear the sound of the alarm. Now if the air inside the vessel is removed completely. How will the loudness of alarm get affected for the same person?

Accepted Answer

Until the air was present in the vessel the necessary medium was there to help the sound to propagate. But when the air is removed from the vessel vacuum takes place. Sound cannot propagate in a vacuum; therefore the man standing next to the vessel will not hear the sound of the bell.

Question 7

Describe an experiment to show that sound can travel in water.

Accepted Answer

Take a tub filled with water. Hold a bell in one hand and dip it in water. Keep one of your ears gently on the surface of water without letting water into the ear. Now ring the bell inside water. You will be able to hear the sound clearly. This shows that sound can travel through liquids.

Question 8

The medium through which the sound travels fastest is empty space.

Accepted Answer

Answer is BSound waves need to travel through a medium such as a solid, liquid, or gas. The sound waves move through each of these mediums by vibrating the molecules in the matter. The molecules in solids are packed very tightly. Liquids are not packed as tightly as solids. And gases are very loosely packed. The spacing of the molecules enables sound to travel much faster through a solid than a gas. Sound travels about four times faster and farther in water than it does in air. Sound waves are travelling vibrations of particles in media such as air, water or metal. So it stands to reason that they cannot travel through empty space, where there are no atoms or molecules to vibrate.Hence, the speed of sound is maximum in solid and it cannot travel through vacuum. Therefore, this statement is false.

Question 9

Describe the bell jar experiment to prove that sound requires a medium to propagate.

Accepted Answer

Bell Jar Experiment : Let us take a bell jar and suspend an electric bell in it and connect it to a battery outside the jar When the circuit is closed (switch is on) we can hear the bell ringing as the jar contains air and sound travels through this airWe then remove the air from the jar with the help of a vacuum pump connected to the bell jar Now as we close the circuit we can hardly hear any sound even though the hammer of the bell is seen striking the gong So we can conclude that sound cannot propagate in the absence of the material medium

Question 10

Which of the following statements is wrong?

Accepted Answer

First three options are fact related to sound properties.1. It travels in a straight line2. It travels as a wave3. A sound is a form of energy4. Soundwave follows the laws of reflection. It needs a material medium for the propagation. so, it cannot travel in a vacuum.So option D is the wrong w.r.t sound

Revise with Concepts

Sound Needs Medium

Quick Summary With Stories

Sound Needs a Medium for Propagation

Bell Jar Experiment