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 free, damped and forced oscillations free, forced and damped oscillations oscillations oscillation and waves physics

The tendency of one object to force another adjoining or interconnected object into vibration motion is referred to as a 

  1. forced vibration.

  2. damped vibration

  3. loudness

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

The tendency of one object to force another adjoining or interconnected object into vibrating motion is referred to as a forced oscillation.

Multiple choice free, damped and forced oscillations free, forced and damped oscillations oscillations oscillation and waves physics

If a force is continually or repeatedly applied to keep the oscillation going, it is called 

  1. forced oscillator.

  2. free oscillatior

  3. damped oscillatior

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

When a periodically repetitive and oscillatory force acts on an object, then the object is forced to oscillate with the frequency of the periodic force. Such oscillation is known as forced oscillation. When an object is displaced from its mean position and allowed to vibrate along its mean position then the object vibrates with its own natural frequency. This is known as free vibration or oscillation. And an oscillation in which the amplitude goes on decreasing with time is known as damped oscillation.

Multiple choice free, damped and forced oscillations free, forced and damped oscillations oscillations oscillation and waves physics

When we push a child in a swing, the amplitude of the oscillation

  1. decreases

  2. increases

  3. remains same

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

By pushing a child on a swing a driving force is applied which forces the swing and the child in the forward direction. The gravitational force acts as a restoring force and pulls back the child to the original position. These two forces together set them into an oscillatory motion. By pushing the child the amplitude, that is the maximum displacement, increases.

Multiple choice free, damped and forced oscillations free, forced and damped oscillations oscillations oscillation and waves physics

A motion caused by an unbalanced rotating component is an example of

  1. free vibration

  2. forced vibration

  3. natural vibration

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A motion of an unbalanced rotating component is an example of forced vibration. As to rotate it with the unbalanced condition some external agent is required.

Multiple choice free, damped and forced oscillations free, forced and damped oscillations oscillations oscillation and waves physics

Which of the following is/are the correct option(s)?

  1. A louder sound is always produced when an accompanying object of smaller surface area is forced into vibration at the same natural frequency.

  2. A louder sound is always produced when an accompanying object of greater surface area is forced into vibration at the different natural frequency.

  3. A louder sound is always produced when an accompanying object of greater surface area is forced into vibration at the same natural frequency.

  4. A louder sound is always produced when an accompanying object of smaller surface area is forced into vibration at the different natural frequency.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Statement C is true, consider the case of a guitar string mounted to the sound box. The fact that the sound box is greater than the surface area of the string means more surrounding particles will be forced into vibration causes an increase in amplitude and loudness.

Multiple choice physics option b: engineering physics introduction to sound free, forced and damped oscillations resonance

Assertion (A): In damped vibrations, amplitude of oscillation decreases
Reason (R): Damped vibrations indicate loss of energy due to air resistance

  1. Both A and R are true and R is the correct explanation of A

  2. Both A and R are true and R is not the correct explanation of A

  3. A is true and R is false

  4. A is false and R is true
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Damped vibrations in which an oscillating system has the effect of reducing, restricting or preventing its oscillations.

Multiple choice geography our changing earth earthquake and volcanoes earthquake earthquakes

An earthquake produces which kind of sound before the main shock wave begins?

  1. Ultrasound

  2. Infrasound

  3. Audible sound

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

Earthquake is a movement of tremor of the earth's crust. It originated naturally and below the surface. An earthquake produces infrasound before the mainshock wave begins. Infrasound is low-frequency sound less than 20hz. It can travel hundreds of km through the earth's surface. So by detecting this sound, we can predict an earthquake.

Multiple choice speed of sound in gas speed of a travelling wave oscillation and waves waves physics

Two open pipes of length $20$ cm and $20.1$ cm produces $10$ beats/s. The velocity of sound in the gas is 

  1. $804 ms^{-1}$
  2. $402 ms^{-1}$
  3. $420 ms^{-1}$
  4. $330 ms^{-1}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For an open pipe, frequency f = v / (2L). Beats = f1 - f2 = (v/2) * (1/L1 - 1/L2). Substituting L1 = 0.2m, L2 = 0.201m, and beats = 10, we get 10 = (v/2) * (1/0.2 - 1/0.201) = (v/2) * (0.001 / 0.0402). Solving for v gives 402 m/s.

Multiple choice speed of sound in gas speed of a travelling wave oscillation and waves waves physics

The formula proposed by Newton for velocity of sound in air is based on _________ process.

  1. adiabatic

  2. isothermal

  3. isochoric

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

According to Newton, when sound waves propagate in air, compression and rarefaction are formed. He assumed that the process is very slow and the heat produced during compression is given to surrounding and heat loss during compression is gained from surrounding. So the temperature remains constant and sound waves propagate through an isothermal process. 

so the answer is B.

Multiple choice speed of sound in gas speed of a travelling wave oscillation and waves waves physics

Two sound waves of angular frequencies $\omega _{1}$ and $\omega _{2}$ move in the same direction. If the under-root of ratio of average power transmitted across a cross-section by them is a and the ratio of their pressure amplitude is $b$, find the ratio of their frequencies of vibrations?

  1. $\dfrac {a\omega _{1}}{b\omega _{2}}$
  2. $\dfrac {ab\omega _{1}}{\omega _{2}}$
  3. $\dfrac {b\omega _{1}}{a\omega _{2}}$
  4. $\dfrac {\omega _{1}}{ab\omega _{2}}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Power P is proportional to (pressure amplitude)^2 * frequency^2. Given sqrt(P1/P2) = a and (deltaP1/deltaP2) = b, then (a)^2 = (b)^2 * (omega1/omega2)^2. Rearranging gives omega1/omega2 = a/b. The ratio of frequencies is proportional to the ratio of angular frequencies.