Lakhmir Singh Solutions - Physics- Class 9 solutions for Chapter 5 Sound

Can sound travel through

a) iron

b) water?

Can sound travel through a vacuum?

Name the type of waves that are used by astronauts to communicate with one another on the moon.

Name one solid, one liquid, and one gas through which sound can travel.

Which of the following cannot transmit sound?

Water, vacuum, aluminum, oxygen gas

Name the physical quantity whose SI unit is ‘hertz’.

What is the SI unit of frequency?

What type of wave is represented:

a) by density-distance graph?

b) by the displacement-distance graph?

Is the speed of sound more in water or in steel?

In which medium sound travels faster: air or iron?

In which medium sound travels fastest: air, water, or steel?

Out of solids, liquids, and gases:

a) in which medium sound travels slowest?

b) in which medium sound travels fastest?

Which of the following is the speed of sound in copper and which in aluminum?

a) 5100 m/s

b) 1500 m/s

c) 3750 m/s

If you want to hear a train approaching from far away, why is it more convenient to put the ear to the track?

What is the speed of sound:

a) in air

b) in water

c) in iron

What name is given to those aircrafts which fly at speeds greater than the speed of sound?

A jet aircraft flies at a speed of 410 m/s. What is this speed known as?

What is meant by supersonic speed?

State one observation from everyday life which shows that sound travels much more slowly than light.

Name the two types of waves that can be generated in a long flexible spring.

A stone is dropped on the surface of the water in a pond. Name the type of waves produced.

Name the type of waves produced when a tuning fork is a truck in the air

What is the general name of the waves consisting of:

a) compressions and rarefactions

b) crests and troughs

What type of waves are illustrated by the movement of a rope whose one end is fixed to a pole and the other end is moved up and down?

What should an object do to produce sound?

What is the name of the strings which vibrate in our voice box when we talk?

Name the device which is used to produce sound in laboratory experiments.

What is the nature of sound waves in air?

What conclusion can be obtained from the observation that when the prongs of a sound-making tuning fork touch the surface of the water in a beaker, the water gets splashed?

State whether the following statement is true or false:

The sound produced by a vibrating body travels to our ears by the actual movement of air.

Which of the following travels slowest in air and which one fastest:

Supersonic aircraft, light, sound

Which term is used to denote a speed greater than the speed of sound?

In which medium sound travels faster: air or hydrogen?

A tuning fork has a number 256 marked on it. What does this number signify?

What is the time-period of a tuning fork whose frequency is 200 Hz?

Calculate the frequency of a wave whose time-period is 0.02s.

What will be the change in the wavelength of a sound wave in the air if its frequency is doubled?

If 20 waves are produced per second, what is the frequency in hertz?

Fill in the blanks with suitable words:

a) Sound is caused by _______

b) A sound wave consists of places of higher pressure called _______ and places of _______ pressure called _______

c) Wave speed in meters per second equals frequency in ______ multiplied by _______ in ________

d) Sound cannot travel through _______

e) The speed of sound in a solid is _______ than the speed of sound in air.

f) When the frequency of the sound is increased, the wavelength ________

What is vacuum? Explain why sound cannot travel through vacuum?

Explain the term ‘amplitude’ of a wave. Draw the diagram of a wave and mark its amplitude on it.

a) Distinguish between longitudinal and transverse waves.

b) Are sound waves longitudinal or transverse?

A cricket ball is seen to hit the bat first and the sound of hitting is heard a little later. Why?

Explain why the flash of lightning reaches us first and the sound of thunder is heard a little later.

Explain why the flash of a gun shot reaches us before the sound of the gun shot

Which of the following terms apply to sound waves in air and which to water waves?

Transverse, rarefaction, trough, crest, compression, longitudinal

a) Name four ways in which sound can be produced.

b) Calculate the speed of a sound wave whose frequency is 2 kHz and wavelength 65 cm.

If a ringing bicycle bell is held tightly by the hand, it stops producing sound. Why?

Which object is vibrating when the following sounds are produced?

a) the sound of a sitar

b) the sound of a table

c) the sound of a tuning fork

d) the buzzing of a bee or mosquito

e) the sound of a flute

Give a reason for the following:

In most of the cases, we cannot see the vibrations of sound-producing objects with our eyes.

Describe a simple experiment to show that the prongs of a sound producing tuning fork are vibrating.

When we open a gas tap for a few seconds, the sound of escaping gas is heard first but the smell of gas comes later. Why?

A sound signal of 128 vibrations per second has a wavelength of 2.7m. Calculate the speed with which the wave travels.

A wave is moving in the air with a velocity of 340 m/s. Calculate the wavelength if its frequency is 512 vibrations/sec.

Define the ‘frequency’ and ‘time period’ of a wave. What is the relation between the two?

Explain why a ringing bell suspended in a vacuum chamber cannot be heard outside.

The frequency of the sound emitted by the loudspeaker is 1020Hz. Calculate the wavelength of the sound wave in air inn cm where its velocity is 340 m/s.

What is the difference between a compression and a rarefaction in a sound wave? Illustrate your answer with a sketch.

a) What is sound? What type of waves are sound waves in air?

b) Describe an experiment to show that sound cannot pass through vacuum.

a) How is the sound produced? Explain with the help of an example.

b) How does sound from a sound-producing body travel through the air to reach our ears? Illustrate your answer with the help of a labelled diagram

a) An electric bell is suspended by thin wires in a glass vessel and set ringing. Describe and explain what happens if the air is gradually pumped out of the glass vessel.

b) Why cannot a sound be heard on the moon? How do astronauts talk to one another on the surface of the moon?

a) Define the terms ‘frequency’, ‘wavelength’, and ‘velocity’ of a sound wave. What is the relation between them?

b) A body vibrating with a time period of 1/256 s produces a sound wave which travels in the air with a velocity of 350 m/s. Calculate the wavelength.

a) What are longitudinal waves and transverse waves? Explain with the help of labelled diagrams.

b) Give two examples each of longitudinal waves and transverse waves.

a) Explain the terms ‘compression’ and ‘rarefactions’ of a wave. What type of waves consists of compression and rarefaction?

b) A worker lives at a distance of 1.32 km from the factory. If the speed of sound in the air be 330 m/s how much time will the sound of factory siren take to reach the worker?

a) Explain the terms ‘crests’ and ‘trough’ of a wave? What type of waves consists of crests and troughs?

b) The flash of a gun is seen by a man 3 seconds before the sound is heard. Calculate the distance of the gun from the man.

a) When we put our ear to a railway line, we can hear the sound of an approaching train even when the train is far off but its sound cannot be heard through the air. Why?

b) How could you convince a small child that when you speak, it is not necessary for air to travel from your mouth to the ear of a listener?

Which of the following statement best describes frequency?

a) the maximum disturbance caused by a wave

b) the number of complete vibrations per second

c) the distance between one crest of a wave and the next one

d) the distance travelled by a wave per second

Which of the following vibrates when a musical note is produced by the cymbals in an orchestra?

a) stretched strings

b) stretched membranes

c) metal plates

d) air columns

If the speed of a wave is 340 m/s and its frequency is 1700 Hz, then λ for this wave in cm will be:

a) 2

b) 0.2

c) 20

d) 200

A musical instrument is producing a continuous note. This note cannot be heard by a person having a normal hearing range. This note must then be passing through:

a) water

b) wax

c) vacuum

d) empty vessel

Which one of the following does not consist of transverse waves?

a) light emitted by a CFL

b) TV signals from a satellite

c) ripples on the surface of a pond

d) musical notes of an orchestra

Sound travels in the air:

a) if particles of medium travel from one place to another

b) if there is no moisture in the atmosphere

c) if disturbance moves

d) if both, particles as well as disturbance move from one place to another

In the sound wave produced by a vibrating tuning fork shown in the diagram, half the wavelength is represented by:

a) AB

b) BD

c) DE

d) AE

The maximum speed of vibrations which produce audible sound will be in:

a) dry air

b) seawater

c) ground glass

d) human blood

The sound waves travel fastest:

a) in solids

b) in liquids

c) in gases

d) in vacuum

The speeds of sound in four different media are given below. Which of the following is the most likely speed in m/s with which the two under water whales in a sea talk to each other when separated by a large distance?

a) 340

b) 5170

c) 1280

d) 1530

When the pitch of the note produced by a harmonium is lowered, then the wavelength of the note: a) decreases b) first decreases and then increases c) increases d) remains the same

The velocities of sound waves in four media P, Q, R, and S are 18000 km/h, 900 km/h, 0 km/h, and 1200 km/h respectively. Which medium could be a liquid substance?

a) P

b) Q

c) R

d) S

Which of the following can produce longitudinal waves as well as transverse waves under different

conditions?

a) water

b) TV transmitter

c) slinky

d) tuning fork

Lakhmir singh solutions physics class 9 Solutions for Chapter 5 sound