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

How does a sound making object differ from one that is silent?

  1. sound making objects vibrate

  2. sound making objects oscillates

  3. sound making objects shows up and down motion

  4. none
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Sound making object can vibrate easily.a vibrating body produces sound when a body vibrates, then the particles of the medium around the object are set into vibrations.

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

Explain why, if we strike a table lightly, we hear a soft sound but if we hit the table hard, a loud sound is heard.

  1. when a table is striked lightly, vibrations are produced with less amplitude.

  2. when the table is strikes hard, the amplitude is high.

  3. both A and B

  4. none
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

If we strike a table lightly the vibrations produced have less amplitude than when we strike the table hard. Since loudness depends on amplitude, soft sound is heard when we strike lightly.

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

Hertz stands for number of oscillations per:

  1. Second

  2. Minute

  3. Hour

  4. Milli second
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Hz is the SI unit of frequency which is defined as wave cycles per unit time..  Since SI unit of time is second. Hz is number of wave cycles per second.

So the answer is A.

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 has a frequency of $10$kHz and wavelength $3$mm. How much time will it take to travel $3$ metre?

  1. $0.1$ sec
  2. $1$ sec
  3. $10$ sec
  4. $0.01$ sec
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$V=f\times \lambda$
$=10\times 10^3\times 3\times 10^{-3}=30$
$t=\displaystyle\frac{d}{v}=\frac{3}{30}=0.1$sec.

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 time period of a system executing wave motion depends upon

  1. elasticity

  2. inertia

  3. Amplitude

  4. restoring force
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Time period of oscillations is directly proportional to square root of modulus of elasticity and inversely proportional to density. Thus option (a) is the correct option

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 total energy of sound waves E is related to their frequency n as

  1. $E \propto n$
  2. $E \propto \dfrac{1}{n}$
  3. $E \propto \dfrac{1}{n^2}$
  4. $E \propto \dfrac{1}{log n}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Energy of a wave is related to its frequency using the formula E = hf, f is the frequency of the wave

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

Two tuning forks of frequency 256 and 258 vibrating per second are sounded together, then time interval between consecutive maxima heard by the observer is.

  1. 2 sec

  2. 1 sec

  3. 0.5 sec

  4. 1/4 sec
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\begin{array}{l} { n _{ 1 } }=256 \ { n _{ 2 } }=258 \ Both\, tuning\, forks\, are\, making\, beats \ so,\, we\, know\, that \ { t _{ \left( { for\, \, \max  . } \right)  } }=\dfrac { 1 }{ { { n _{ 2 } }-{ n _{ 1 } } } } \sec   \ =\dfrac { 1 }{ { 258-256 } }  \ =0.5\, \sec   \end{array}$

Hence, the option $C$ is the correct answer.

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

If the frequency of sound wave in air is doubled, its wavelength.

  1. is doubled

  2. increases 4 times

  3. decreases 4 times

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

Answer is D.

A sound wave has a speed that is mathematically related to the frequency and the wavelength of the wave. The mathematical relationship between speed, frequency and wavelength is given by the following equation.
Speed = Wavelength * Frequency
That is, Frequency = speed / Wavelength. The frequency and wavelength are inversely proportional to each other.
So, when the frequency is doubled, the wavelength will be halved.

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 time period of a sound wave from a piano is $1.18\times10^{-3} s$. Find its frequency.

  1. $847.45 Hz$
  2. $800 Hz$
  3. $935. 55 Hz$
  4. $1000 Hz$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The frequency (f) of a wave is the number of full wave forms generated per second. This is the same as the number of repetitions per second or the number of oscillations per second.  
Time Period (T) is the number of seconds per waveform, or the number of seconds per oscillation.  It is clear that frequency and period are reciprocals. 
In this case, the time period is given as $1.18\times { 10 }^{ -3 }s$.
So, the frequency $f=\frac { 1 }{ t } =\frac { 1 }{ 0.00118s } =847.45Hz.$

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

In an open pipe pressure at the ends of the pipe is

  1. minimum

  2. maximum

  3. zero

  4. depending on temperature, it can be maximum or minimum.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In an open pipe, the ends are pressure nodes (displacement antinodes) because they are open to the atmosphere, meaning the pressure variation is zero relative to atmospheric pressure.

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

If a vibrator strikes the water $50$ times in $5s$, then the frequency of wave is

  1. $10 Hz$
  2. $0.5 Hz$
  3. $5 Hz$
  4. $0.1 Hz$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Total number of vibrations, in $5s$ is $50$.
So, number of vibrations in $1s$ is $\dfrac{50}{5}=10$
Frequency$=10Hz$
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

One sound wave strikes a person's ear every $1/100$ of a second. The speed of sound where the person is located is $345 m/s$.
What is the frequency of the sound?

  1. $3.45\ Hz$
  2. $34,500\ Hz$
  3. $0.01\ Hz$
  4. $100\ Hz$
  5. $2.9\ Hz$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Time period of sound wave       $T = \dfrac{1}{100}$ second


$\therefore$ Frequency of sound wave      $\nu = \dfrac{1}{T} =100$  $Hz$

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

If you go on increasing the stretching force on a wire in a guitar, its frequency

  1. Increases

  2. Decreases

  3. Remains unchanged

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

When a stretching force is applied to a string or a wire, it applies a restoring force in the opposite direction. This force tends to bring the wire in its original length. It is known as tension in wire.

When we apply a stretching force on the wire of a guitar, the wire applies tension backwards. Greater the stretching force, greater is the tension.
The frequency of vibration of a stretched wire is directly proportional to the square root of the tension in it.
Hence on increasing the stretching force on a wire in a guitar, its frequency increases

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 sounds having frequency of $20$ Hz to $20,000$ Hz are

  1. Ultrasound

  2. Infrasonics

  3. Hypersonics

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

In the case of sound waves, having frequency in between $20$ Hz and $20,000$ Hz, called audible sound and  waves of frequency smaller than $20$ Hz are called infrasonic and waves having frequency greater then $20,000$ Hz, called Hypersonics sounds.

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 oscillator is producing FM waves of frequency 2kHz with avariation of 10kHz. The modulating index=?

  1. 0.20

  2. 5.0

  3. 0.67

  4. 1.5
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Modulation Index , $m _f=\dfrac{\text{Maximum frequency deviation}}{\text{Modulating frequency}}$

$\Rightarrow m _f= \dfrac{10 kHz}{2 kHz}$
$\Rightarrow m _f=5$