One word answer.

Question 11 Mark

What is the audible range of the average human ear?

Answer

The audible range of an average human ear lies between 20Hz to 20,000Hz.
Humans cannot hear sounds having frequency less than 20Hz and greater than 20,000Hz.

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Question 21 Mark

In which of the three media, air, water or iron, does sound travel the fastest at a particular temperature?

Answer

Sound travels fastest in iron as compared to water and air. An echo is returned in 3s. mat is the distance of the reflecting surface from the source, given the speed of sound is 342ms^-1.

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Question 31 Mark

Why are sound waves called mechanical waves?

Answer

Sound waves needs material medium to propagate therefore, they are called mechanical waves. Sound waves propagate through a medium because of the interaction of the particles present in that medium.

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Question 41 Mark

Explain how sound is produced by your school bell.

Answer

When the school bell vibrates, it forces the adjacent particles in air to vibrate. This disturbance gives rise to a wave and when the bell moves forward, it pushes the air in front of it. This creates a region of high pressures known as compression. When the bell moves backwards, it creates a region of low pressure know as rarefaction. As the bell continues to move forward and backward, it produces a series of compressions and rarefactions. This makes the sound of a bell propagate through air.

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Question 51 Mark

What is sound and how is it produced?

Answer

Sound is produced by vibration. When a body vibrates, it forces the neighbouring particles of the medium to vibrate. This creates a disturbance in the medium, which travels in the form of waves. This disturbance, when reaches the ear, produces sound.

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Question 61 Mark

What type of sound waves are produced by a vibrating simple pendulum?

Answer

Infrasonic sound waves.

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Question 71 Mark

Name that part of ear which vibrates when outside sound falls on it.

Answer

Ear drum starts vibrating when outside sound falls on it.

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Question 81 Mark

Name the type of wave produced when a tuning fork is struck in air.

Answer

Longitudinal (sound) waves.

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Question 91 Mark

Name the organs of hearing in our body.

Answer

Ears enable us to hear sounds.

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Question 101 Mark

Which physical quantity remains unchanged after reflection of a sound wave?

Answer

Wavelength, frequency and speed of the sound waves remain the same.

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Question 111 Mark

What is the function of three tiny bones in the ear?

Answer

The function of three tiny bones in the ear is to increase the strength of vibrations coming from the ear drum before passing them onto the inner ear.

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Question 121 Mark

Given below are some example of wave motion. State in case, if the wave motion is transverse, longitudinal or a combination of both?
Waves produced by a motor boat sailing in water.

Answer

Combination of transverse and longitudinal.

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Question 131 Mark

What type of scans are used these days to monitor the growth of developing baby in the uterus of the mother?

Answer

Ultrasound scans are used to monitor the growth of developing baby in the uterus of the mother.

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Question 141 Mark

Given below are some example of wave motion. State in case, if the wave motion is transverse, longitudinal or a combination of both?
Motion of a kink in a long coil spring produced by displacing one end of the string side ways.

Answer

Transverse, because the vibration of particles of the spring are at right angles to the direction of wave propagation.

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Question 151 Mark

Give the principle involved in megaphone.

Answer

Megaphone works on the principle of multiple reflection of sound. A Megaphone works by forcing the sound that comes from a person's voice into one direction making it louder.

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Question 161 Mark

Choose the infrasonic waves and ultrasonic waves from the following frequencies: (i) 10,000Hz (ii) 30,000Hz (iii) 18Hz (iv) 50,000Hz (v) 10Hz

Answer

Infrasonic waves: 10Hz, 18Hz
Ultrasonic waves: 30,000Hz, 50,000Hz

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Question 171 Mark

A bomb explodes on the moon. How long will it take for the sound to reach the earth?

10 seconds
1000 seconds
1 day
None of these

Answer

None of these

Explanation:

Hint: Sound is a mechanical wave and need a medium to propagate.

Explanation:

Sound is a mechanical wave and hence it needs a medium to propagate and the outer space has vacuum and therefore if a bomb explodes on the moon its sound will never reach the Earth.

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Question 181 Mark

Name the three characteristic of sound.

Answer

Loudness.
Pitch.
Timbre or Quality.

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Question 191 Mark

Which of the following travels slowest in air and which one fastest?
Supersonic aircraft, Light, Sound.

Answer

Slowest - Sound
Fastest - light

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Question 201 Mark

Name three devices which work on the reflection of sound.

Answer

Megaphone and bulb horn.
Stethoscope.
Soundboard.

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Question 211 Mark

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

Answer

Solid - table.
Liquid - water.
Gas - air.

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Question 221 Mark

Name the characteristic of sound which depends on (a) amplitude (b) frequency, and (c) waveform.

Answer

Loudness.
Pitch.
Timbre.

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Question 231 Mark

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

5100m/s
1500m/s
3750m/s

Answer

Speed of sound in copper = 3750m/s

Speed of sound in aluminium = 5100m/s

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Question 241 Mark

Which property of sound leads of the formation of echoes?

Answer

The reflection of sound leads to formation of echoes.

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Question 251 Mark

State the general name of the waves on which the particles of the medium vibrate:
At right angles to the direction of wave.

Answer

Transverse waves.

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Question 261 Mark

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

Answer

Transverse (water) waves.

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Question 271 Mark

What happens to the loudness of a sound if its amplitude decrease?

Answer

The loudness decreases with the decrease in the amplitude of sound.

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Question 281 Mark

In which medium, air or water, an echo is heard much sooner? Why?

Answer

An echo is heard sooner in water because the speed of sound in water is higher than the speed of sound in air.

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Question 291 Mark

Out of solids, liquids and gases:
In which medium sound travels slowest?

Answer

Sound travels slowest in gases.

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Question 301 Mark

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

Answer

$\text{Frequency}=\frac{1}{\text{Time period}}$
$=\frac{1}{0.02}=50\text{Hz}$

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Question 311 Mark

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

Answer

The number 256 on tuning fork signifies the frequency of tuning fork.

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Question 321 Mark

What name is given to the repetition of sound caused by the reflection of sound waves?

Answer

Echo is repetition of sound caused by the reflection of sound waves.

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Question 331 Mark

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

Answer

It is more convenient to put the ear to the track to hear a train approaching from far away because sound travels faster in solids than in air.

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Question 341 Mark

Can we hear (a) infrasonic waves (b) ultrasonic waves?

Answer

No, we cannot hear infrasonic waves and ultrasonic waves. That’s because the frequencies of both these waves fall beyond the human audible range of frequencies.

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Question 351 Mark

Can sound travel through (a) iron, and (b) water?

Answer

Yes, sound can travel through iron and as well as water.

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Question 361 Mark

How does the pitch of a sound depend on frequency?

Answer

Pitch of a sound is directly proportional to frequency. Higher the frequency, higher is the pitch of the sound.

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Question 371 Mark

Name the characteristic which helps us distinguish between a man’s voice and woman’s voice, even without seeing them.

Answer

Pitch helps us to distinguish between a man’s voice and a woman’s voice, even without seeing them.

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Question 381 Mark

Name the principle on which a soundboard works.

Answer

Soundboard works on the principle of reflection of sound.

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Question 391 Mark

Name the type of waves which are used by astronauts to communicate with one another on moon (or in outer spece).

Answer

Radio waves are used to communicate with one another on moon.

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Question 401 Mark

Why is the ceiling and wall behind the stage of good conference halls or concert halls made curved?

Answer

Ceiling and walls are made curved so that sound after reflection reaches the all audience euqally in all direction.

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Question 411 Mark

What will increase, if we change feeble sound to loud sound?

Answer

The loudness or softness of a sound is determined basically by its amplitude, so for a loud sound it must have higher amplitude.

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Question 421 Mark

How is pitch of sound related to its frequency?

Answer

The sensation of a frequency is commonly referred to as the pitch of a sound. A high pitch sound corresponds to a high frequency sound wave and a low pitch sound corresponds to a low frequency sound wave.

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Question 431 Mark

In which medium sound travels faster: air or iron?

Answer

Sound travels faster in iron (being a solid medium).

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Question 441 Mark

Which of the two produces ultrasonic waves: porpoise or whale?

Answer

Porpoise produces ultrasonic waves.

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Question 451 Mark