Sound : Complete Set of Questions

This set of questions contains all the possible concepts
which could be asked in the examination

Sound

Q.1 Â What is sound?

Sound is a form of energy emitted by a vibrating object producing sensation of hearing.

Q.2 Â Write any three characteristics of sound waves.

Following are the properties of sound waves:

• These are longitudinal waves.
• These are Mechanical waves.
• These are a result of vibrations.

Q.3 Â Energy can neither be created nor be destroyed it can change from one form to another. Does this law apply to sound too?

Yes, sound being a form of energy is created through another form of energy. For example: when we clap our hands we hear sound, this sound is produced due to conversion of muscular energy of our hand to sound energy.

Q.4 Â What are the different types of sound on the basis of frequencies?

On the basis of frequencies, sound can be:

(a) Infrasound â€“ frequencies below than 20 Hz

(b) Audible sound â€“ frequencies between 20 Hz to 20,000 Hz.

(c) Ultrasound - frequencies above 20,000 Hz

Q.5 Â What is a supersonic speed?

When the speed of an object exceeds the speed of the sound, then the speed with which the body travels is supersonic speed. For example, aircrafts, bullet, etc. which travels at a higher speed than the speed of sound.

Q.6 Â When does a body produce sound?

Sound is produced through the to and fro motion of the particles of the medium in which sound travels. These particles vibrate about their mean position forming disturbances in the form of waves.

Q.7 Â Write a short note on propagation of sound.

Or

Write a short note on how does the sound produced by a vibrating object in a medium reaches our ear.

- When sound is produced by the source, for listener to listen the sound passes through certain medium.

- The vibrating object sets the particles of the medium around it into vibration, to and fro motion.

- A particle in contact with the vibrating object moves towards a particular direction. This particle exerts a force on the nearby particles which displaces from its equilibrium position and starts moving towards the same direction in which the original molecule was travelling. After displacing the second particle, the first particle returns to its original position. Similarly, particle second exerts a force on third particle and so on.

- Like this all the particle in between the source and listener vibrates and the sound is conducted to the listener.

Note - the particles of medium do not actually move from the vibrating body, they just vibrates
the particles.

Q.8 Â What is a medium? What are the different mediums in which sound can travel?

Medium is a substance in which sound travels. Without a medium sound cannot propagate. The different medium through which sound travels is gas, liquid and solids.

Q.9Â Â Â Â Â  Give reason:

(a) Astronauts cannot talk to each other in space.

(b) A bomb explosion on moon cannot be heard.

(a) Since sound waves being mechanical in nature, needs a material medium to travel and in space there is no atmosphere present. So, sound could not be heard in space. To communicate in this environment they use radio waves, a type of electromagnetic wave which do not use mediumÂ for its propagation.

(b)Â Since moon does not have atmosphere or a medium in which sound can travel so, if there occurs a bomb explosion on moon, it could not be heard by the persons even present on the moon.

Q.10 Â Which device is used to measure intensity of earthquake?

Seismometers

Q.11 Â What is decibel?

The intensity of a sound is measured in a unit known as decibel which is denoted by dB.

Q.12 Â Sound waves cannot travel through vacuum. Explain.

Sound waves cannot travel through vacuum as these are mechanical waves and needs a material medium to travel.

Q.13 Â (a) What is amplitude?

(b) Name the characteristics of sound.

(a) Amplitude of a wave is the maximum displacement of the particles of the medium from their mean position when a wave passes through the medium. It is denoted by A. the SI unit is metre(m).

(b) The characteristics of sound are:Â Â

(i) Loudness

(ii) Pitch or Shrillness

(iii) Quality or timbre

Q.14 Â On which factors does the speed of sound depend?

Underneath are the factors which have an effect on speed of the sound:

(a) Density of the medium through which sound travels: With the increase in density of medium the speed of sound also increases. i.e. Speed of sound in solids>speed of sound in liquids> speed of sound in air.

(b) Temperature: The speed of sound increases with the increase in the temperature i.e. with every 1o increase in temperature the speed of sound increases by 0.6 m/s.

(c) Humidity of air: As the humidity of air increase the speed of sound also increases.Â

Q.15 Â We hear two distinct sounds when a person strikes a hammer on the railway lines from a distance. Why is it so?

We hear two distinct sounds, when one hammer on the railway line from a distance because due to the striking of hammer the wave produced would travel by two routes one through solid and other through air. Since the speed of sound in air is different from speed of sound in solid, there would be two distinct sounds heard by the listener.

Q.16 Â Give reasons:

(a) Sound travels faster in summer than in winter.

(b) Two friends on the surface of the moon cannot talk to each other.

(c) Presence of an advancing train is felt by sticking our ears to rail lines before its sound approaches to the listener by air.

(a) Sound travels faster in summer season than in winter season because, with the increase in temperature speed of sound also increases and in summers temperature is high with respect to the winters.

(b)Â Two friends on the surface of the moon cannot talk to each other because moon does not have atmosphere or medium for sound to propagate so sound would not produce.

(c)Â Speed of sound depends upon the density of medium in which it travels. Speed of sound will be greater in substances with greater density i.e. speed of sound in solids > speed of sound in liquids > speed of sound in air. Since rails are made of metal (solid) sound would travel faster in ails than in air (gas).Â

Q.17 Â Two persons are holding an iron rod. First person knocked the rod by a hammer. What will be the ratio of times taken by the sound wave in air and in iron to reach the second person?

Suppose, l = length of the iron rod

Time taken by the sound to travel through the iron rod is given by

${t_1} = {{Distance} \over {Speed}} = {l \over {{V_{Iron}}}}$

Similarly, time taken by the sound to travel through the air is given by

${t_2} = {{Distance} \over {Speed}} = {l \over {{V_{air}}}}$

Therefore, ratio of time taken by the sound wave in Air and Iron

${t_1}:{t_2} = {{{V_{air}}} \over {{V_{Iron}}}}$

Q.18 Â Why is noise different from music?

Q.19 Â Define the terms: (a) Tone (b) Note

(a)Â Tone: A sound produced by single frequency is known as tone.

(b) Note: A sound produced by mixture of frequencies is known as note.

Q.20 Â What changes occurs in the speed of sound when

(a) It travels from iron to air?

(b) Temperature of the air increases?

(a) Speed of sound decreases when sound waves travel from a solid state to gaseous.

(b) With the rise in temperature of air, the speed of sound travelling in it increases.

Q.21 Â With the help of an experiment show that sound needs a material medium for its propagation.

System:

• Suspend an electric bell in an airtight glass bell jar packed with a cork.
• The bell jar is connected to a vacuum pump, from the bottom.

Experiment:

• Press the switch ON, the bell would be heard.
• Now start the vacuum pump.
• With the decrease in the air in the jar through vacuum pump the sound would become paler, with current being flowing constantly.
• When entire air will be removed then no sound will be heard.

Inference:

• Sound needs a material medium to propagate.

Q.22 Â Three friends are made to hear a sound travelling through different media as given below:

Which one will hear the sound first? Andwhy?

Speed of sound in solids > Speed of sound in liquids > Speed of sound in gases

Speed of sound depends upon the elasticity and density of a medium. More the density more is the speed of sound.

Therefore, sound will travel fastest in steel and slowest in oxygen. So, Riya would hear the sound

first.

Q.23 Â Show the propagation of a longitudinal wave showing compression and rarefaction.

Compression are denoted by Â â†’ A, C, E, G

Rarefaction are denoted by â†’ B, D, F

Q.24 Â Differentiate between Loudness and Intensity.

Q.25 Â State the mechanism through which humans can utter sound through their mouth.

The sound produced by our speech is produced through the vibrations of the two vocal cords present in our throat. This vibration is caused by the air approaching from the lungs.

Q.26 Â Name the characteristic of sound involved when a baby distinguishes her motherâ€™s voice with others.

Quality or timber is the characteristic of sound involved here.

Q.27 Give reason for the following:

(a) We hear the sound of a horn of approaching car before the car reaches us.

(b) We hear the sound produced by the humming bees while the sound of vibration of pendulums is not heard.

(c) Â This is so as the speed of car is much less than that of the sound. So, sound of horn travels faster than the car itself and we can hear the sound earlier than actually see the car.

(d) Â This is so as the sound produced by the humming of a bee is in the audible range of our hearing unlike the pendulum, which is so low to be heard by humans.

Q.28 Â How is sound produced when our school bell is struck with a hammer?

Sound is produced when the school bell is struck by the hammer. As this happens the bell starts vibrating. These vibrations then produce disturbances in air, which travels as sound waves to our ear.

Q.29 Â Define the term:

(a) Loudness

(b) Intensity

(c) Pitch

(d) Quality

(a) Loudness: it is the feeling produced in the ear which helps us to differentiate between a loud and a dim sound. The loudness or softness of sound depends upon the amplitude of the wave. The soft sound has small amplitude and louder sound has large amplitude.

(b) Â Intensity: it is the amount of energy passing at every second through a unit area.

(c) Â Pitch: it is the characteristic of sound which helps in differentiating between a harsh sound and a dull sound. It depends upon the frequency of vibration. Low pitch sound have low frequency and high pitch sound have high frequency.

(d) Â Quality: it is the characteristic of sound which differentiate between the two waves of having same pitch and loudness.