Physics · Science General

Acoustics and Sound Waves

2,006 Questions

Acoustics and sound waves deal with mechanical vibrations traveling through media like air and water. Key concepts include wave reflection, beats, echoes, the Mach number, and infrasound. These physics fundamentals are regularly tested in general science sections of multiple competitive exams.

Sound wave propagationEchoes and reflectionWave interferenceMach numberInfrasound frequency

Acoustics and Sound Waves Questions

Multiple choice physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

Which of the following can be true?

  1. The instantaneous power output of an ac source can be negative.

  2. The average power output of an ac source can be negative.

  3. The instantaneous power output of an ac source can NOT be negative.

  4. The average power output of an ac source can NOT be negative.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In an AC circuit, the instantaneous power p = v*i can be negative if the voltage and current have opposite signs, which occurs when the phase difference is between 90 and 270 degrees.

Multiple choice physics sound: production of sound oscillation - amplitude, time period and frequency of oscillation time period, frequency and amplitude of sound oscillatory and periodic motion

When sound wave is refracted from air to water, which of the following will remain unchanged?

  1. wave number

  2. wavelength

  3. wave velocity

  4. frequency
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Frequency of a wave is characterised by the source of wave, therefore it will not be affected by change in medium . 

Multiple choice physics sound: production of sound oscillation - amplitude, time period and frequency of oscillation time period, frequency and amplitude of sound oscillatory and periodic motion

Ultrasound has frequency of vibration .....

  1. between 20 Hz and 20000 Hz.

  2. below 20 Hz.

  3. above 20000 Hz.

  4. between 500 Hz and 10000 Hz.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The term "Ultrasound" refers to the sound having frequency greater than the human audible frequency. Maximum limit of the human audible sound is $20000$ Hz.

So, ultrasound has  frequency of vibration above $20000$ Hz.

Multiple choice physics sound: production of sound oscillation - amplitude, time period and frequency of oscillation time period, frequency and amplitude of sound oscillatory and periodic motion

1 Hz is:

  1. 1 vibration per minute.

  2. 360 vibration per minute.

  3. 10 vibration per minute.

  4. 60 vibration per minute.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Frequency of 1 Hz implies to 1 complete vibration per second. This means, 60 complete vibrations in 60 second, or, in 1 minute.

Multiple choice physics sound: production of sound oscillation - amplitude, time period and frequency of oscillation time period, frequency and amplitude of sound oscillatory and periodic motion

An object oscillates 50 times in one second. What would be its frequency?

  1. 0.2 hz

  2. 0.02 hz

  3. 0.002hz

  4. 50Hz
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Frequency is defined as the number of oscillations in one second , as the given object is oscillating , 50 times in one second therefore its frequency is 50 Hz .

Multiple choice physics sound: production of sound oscillation - amplitude, time period and frequency of oscillation time period, frequency and amplitude of sound oscillatory and periodic motion

The sound from a mosquito is produced when it vibrates its wings at an average rate of $500$ vibrations per second. What is the time period of the vibration?

  1. 0.001

  2. 0.002

  3. 0.003

  4. 0.004
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Frequency equals the number of waves that passes a given point per second or the number of oscillations of a vibrating body per second or number of cycles per second.
In this case, a mosquito vibrates its wings at an average rate of 500 vibrations per second. Therefore, the frequency of the sound is 500 Hz.
Time period of the wave is defined as the reciprocal of the frequency of the wave.
That is, $T=\frac { 1 }{ f } =\frac { 1 }{ 500 } =0.002\quad second$.
Hence, time period of the sound produced by the mosquito is 0.002 second.

Multiple choice physics sound: production of sound oscillation - amplitude, time period and frequency of oscillation time period, frequency and amplitude of sound oscillatory and periodic motion

A sound wave completes $24$ cycles in $0.8\;s$. The time period of the wave would be:

  1. $1/30\;s$
  2. $30\;s$
  3. $1/24\;s$
  4. $24\;s$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A time period is the time taken to complete one cycle.


Given that, the sound wave completes $24$ cycles in $0.8\,s$

So, the time taken to complete one cycle $=\dfrac{0.8}{24}=\dfrac{1}{30}\,s$

Hence the time period is $\dfrac{1}{30}\,s$

Multiple choice physics sound: production of sound oscillation - amplitude, time period and frequency of oscillation time period, frequency and amplitude of sound oscillatory and periodic motion

A man blows a whistle and hears an echo after 1.2 seconds. The distance between the man and the reflector of the sound is _____ m. (take velocity of sound in air as $330 {ms}^{-1}$)

  1. 250

  2. 190

  3. 298

  4. 198
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The total distance traveled by the sound is speed multiplied by time: 330 m/s * 1.2 s = 396 m. Since the sound travels to the reflector and back, the distance to the reflector is half of the total distance: 396 / 2 = 198 m.

Multiple choice physics sound: production of sound oscillation - amplitude, time period and frequency of oscillation time period, frequency and amplitude of sound oscillatory and periodic motion

A source of sound is moving away from an observer at rest with a velocity $50 {ms}^{-1}$. If the frequency of sound is 200 Hz, find the apparent frequency observed by the observer. (Take velocity of sound = $300 {ms}^{-1}$)

  1. 140 Hz

  2. 25.1 Hz

  3. 171.4 Hz

  4. 75.6 Hz
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The apparent frequency is calculated using the Doppler effect formula for a source moving away: f' = f * (v / (v + vs)). Plugging in the values: 200 * (300 / (300 + 50)) = 200 * (300 / 350) = 200 * (6 / 7) = 171.4 Hz.

Multiple choice physics sound: production of sound oscillation - amplitude, time period and frequency of oscillation time period, frequency and amplitude of sound oscillatory and periodic motion

The frequency of sound waves can be expressed in 

  1. Hz
  2. $cycle/second$
  3. $s^{-1}$

  4. all the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The frequency of a wave is the number of waves passing a point in a certain time. The SI unit of frequency is $Hz$. One Hz is equal to one cycle per second.

We also have the relation between the frequency and the time period as:
$f=\frac{1}{T}$
The time is measured in seconds. So the frequency can also be expressed as $s^{-1}$

Multiple choice physics sound: production of sound oscillation - amplitude, time period and frequency of oscillation time period, frequency and amplitude of sound oscillatory and periodic motion

Which of the following sounds have the highest frequency?
a) A man shouting.
b) The sound of a whistle.
c) A lion's roar.
d) The sound of a drum.

  1. a

  2. b

  3. c

  4. d
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Low frequency sounds are low pitched like that of a man shouting, a lion's roar, sound of a drum, etc.

Multiple choice physics sound: production of sound oscillation - amplitude, time period and frequency of oscillation time period, frequency and amplitude of sound oscillatory and periodic motion

Fill in the blank.

Shrillness : ______: : Loudness : Amplitude

  1. Pitch

  2. Speed

  3. Frequency

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The loudness of sound is determined by the amplitude of sound since amplitude is merely the magnitude of sound. Similarly, the shrillness or pitch of a sound is determined by frequency and it is directly proportional to frequency.

Multiple choice physics sound: production of sound oscillation - amplitude, time period and frequency of oscillation time period, frequency and amplitude of sound oscillatory and periodic motion

Which are the most important properties of sound?

  1. Amplitude

  2. Frequency

  3. Loudness

  4. Both A and B
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The two most important properties of sound are amplitude and frequency because amplitude determines the loudness of sound and frequency determines its pitch. The loudness and pitch affect the quality of sound.