Intensity of Sound Waves

Q. The displacement -time graphs for two sound waves $\text{A}$ and $\text{B}$ are shown in the figure. The ratio of their intensities $\frac{I_A}{I_B}$ is equal to

1. $1:4$
2. $1:2$
3. $1:16$
4. $1:1$

Q.

What is the loudness of sound? What factors does it depend on?

Q. A) In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of $2.0\times {10}^{10}\text{Hz}$ and amplitude $48\text{V/m}$. What is the wavelength of the wave? $[c=3\times {10}^{8}m/s.]$

B) In a plane electromagnetic wave, the electric field oscillatessinusoidally at a frequency of $2.0\times {10}^{10}$ and amplitude $48V/m$. What is the amplitude of the oscillating magnetic field? $[c=3\times {10}^{8}m/s.]$

C) In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of $2.0\times {10}^{10}\text{Hz}$ and amplitude $48V/m$. Show that the average energy density of the E field equals the average energy density of the B field. $[c=3\times {10}^{8}m/s]$.

Q. A transverse wave is represented by the equation
$y=y_0\sin \frac{2\pi }{\lambda }(vt-x)$
For what value of $\lambda ,$ the maximum particle velocity is equal to two times the wave velocity?

1. $\lambda =\pi y_0/3$
2. $\lambda =\pi y_0/2$
3. $\lambda =\pi y_0$
4. $\lambda =2\pi y_0$

Q. If the frequency of sound produced by a siren increases from $400\text{Hz}$ to $1200\text{Hz}$ keeping the amplitude constant. The ratio of the intensity of sound produced at frequency $1200\text{Hz}$ and $400\text{Hz}$ will be

1. $1:1$
2. $1:3$
3. $3:1$
4. $9:1$

Q. If at some point, the amplitude of a sound wave becomes double and the frequency becomes one fourth, then at that point, the intensity of sound will:

1. Become double
2. Become half
3. Become one fourth
4. Remain unchnaged

Q. Two monochromatic beams $A$ and $B$ of equal intensity $I$, hit a screen. The number of photons hitting the screen by beam $A$ is twice that by beam $B$. Then what inference can you make about their frequencies?

Q.

Consider a metal exposed to light of wavelength $600nm$. The maximum energy of the electron doubles when light of wavelength $400nm$ is used. Find the work function in $eV$.

Q. The intensity level of two sounds are 100 dB and 50 dB. What is the ratio of their intensities?

1. 
2. 
3. 
4. 

Q.

Suppose A nad B in the previous problem change their positions in such a way that tha line joining them becomes perpendicular to the direction of wind while maintaining the separation x. What will be the time lag B finds between seeing and hearing the drum beasting by A ?

Q. The displacement from the position of equilibrium of a point $4cm$ from a source of sinusoidal oscillations is half the amplitude at the moment $t=\frac{T}{6}\left(T\text{~is the time period}\right)$. Assume that the source was at mean position at $t=0$. The wavelength $\left(\text{in}m\right)$ of the running wave is

Q. A point source of power $50\pi \text{W}$ is producing sound waves of frequency $1876\text{Hz}$. What is the pressure amplitude at a distance $\sqrt{330}\text{m}$ from the point source?
[Speed of sound is $330\text{m/s}$ and density of air is $1{\text{kg/m}}^3$]

1. $6{\text{N/m}}^2$
2. $7{\text{N/m}}^2$
3. $8{\text{N/m}}^2$
4. $5{\text{N/m}}^2$

Q. A person speaking normally produces a sound of intensity 40 dB at a distance of 1 m. If the threshold intensity for reasonable audibility is 20 dB, the maximum distance at which he can be heard clearly is

1. 10 m
2. 20 m
3. 4 m
4. 5 m

Q. Calculate the ratio of intensity of wavetrain A to wavetrain B.

1. $1$
2. $3$
3. $0.5$
4. $4$

Q.

Distinguish between loudness and intensity of sound?

Q. The amplitude of a wave represented by displacement equation $y=\frac{1}{\sqrt{a}}\sin \omega t\pm \frac{1}{\sqrt{b}}\cos \omega t$ will be

1. $\frac{a+b}{ab}$
2. $\sqrt{\frac{a+b}{ab}}$
3. $\frac{\sqrt{a}+\sqrt{b}}{ab}$
4. $\frac{\sqrt{a}\pm \sqrt{b}}{ab}$

Q. A train is moving with a constant speed along a circular track. The engine of the train emits a sound of frequency f. The frequency heard by the guard at the rear end of the train

1. is less than f
2. is greater than f
3. is equal to f
4. may be greater than, less than or equal to f depending on factors like speed of train, length of train and radius of circular track.

Q. A point source emits sound of the same power in all directions in a non-absorbing medium. Two points $P$ and $Q$ are at a distance of $9\text{m}$ and $25\text{m}$ respectively from the source. The ratio of the amplitude of the waves at $P$ and $Q$ is

1. $\frac{3}{5}$
2. $\frac{5}{3}$
3. $\frac{9}{25}$
4. $\frac{25}{9}$

Q. A bomb blast gives a sound of intensity $0.8{\text{W/m}}^2$ and frequency $1.5\text{kHz}$. If the density of air is $1.25{\text{kg/m}}^3$ and speed of sound in air is $330\text{m/s}$, then the amplitude of the sound wave is approximately

1. $4.4\mu \text{m}$
2. $5.5\mu \text{m}$
3. $6.6\mu \text{m}$
4. $7.7\mu \text{m}$

Q.

An ocean wave has an amplitude of $\mathbf{2}\mathbf{.}\mathbf{5}\mathbf{m}\mathbf{}$. Weather conditions suddenly change such that the wave has an amplitude of$\mathbf{5}.\mathbf{0}\mathbf{m}$. The amount of energy transported by the wave is _____.

1. halved

2. doubled

3. quadrupled

4. Remains the same

Q. The displacement of an elastic wave is given by the function $y=3\sin \omega t+4cos\omega t$. where $y$ is in $cm$ and $t$ is in second. Calculate the resultant amplitude.

Q. The equation of diaplacement due to a sound wave is $s=s_0{\text{sin}}^2(\omega t-kx)$. If the bulk modulus of the medium is $B$, then the equation of pressure variation due to that sound is

1. $-Bk{s}_0{\cos }^2(\omega t-kx)$
2. $-Bk{s}_0\sin (2\omega t-2kx)$
3. $Bk{s}_0\sin (2\omega t-2kx)$
4. $Bk{s}_0{\cos }^2(\omega t-kx)$

Q. Figure below shows the wave
$y=A\sin (\omega t-kx)$ at any instant travelling in the $+vex$-direction. What is the slope of the curve at $B$?

1. $kA$
2. $\omega /A$
3. $k/A$
4. $\omega A$

Q. A simple harmonic wave of amplitude $2$ units is travelling along positive $x$-axis. At a given instant, displacement for two different particles on the wave is $1$ unit and $\sqrt{2}$ unit. If the wavelength is $\lambda ,$ the distance between them is $\frac{\lambda }{x}.$ Find $x.$

Q. A straight line source of sound of length $10\text{m}$ emits pulse that travels radially outward from the source. A detector is located at a perpendicular distance of $7\text{m}$ from the source. The total power emitted by the source in the form of sound wave is $2.2\times {10}^4\text{W}$. If the surface area of the acoustic detector is $1.2{\text{cm}}^2$, then the power (in $\text{mW}$) intercepted by the detector is
(Assume waves reaches surface of detector perpendicularly and take $\pi =\frac{22}{7}$)

1. $6$
2. $5$
3. $8$
4. $7$

Q. For a point source of sound, the graph of intensity $\left(I\right)$ versus square of distance from source $\left(r^2\right)$ is best represented by

1. 
2. 
3. 
4. 

Q. An increase in intensity level of 1 dB implies an increase in intensity of (given anti $lo{g}_{10}0.1=1.2589)$

1. 
2. 
3. 
4. 

Q. Find the displacement amplitude of particles of air of density $1.5{\text{kg/m}}^3$ if the intensity and frequency of sound are $8\times {10}^{-6}{\text{W/m}}^2$ and $5000\text{Hz}$ respectively.
[speed of sound in air $=330\text{m/s}$]

1. $5.7\text{nm}$
2. $4.7\text{nm}$
3. $3.7\text{nm}$
4. $2.7\text{nm}$

Q. With what velocity an observer should move relative to a stationary source so that he hears a sound of double the frequency of source?

1. Half the velocity of sound towards the source
2. Double the velocity of sound towards the source
   
3. Velocity of sound towards the source
4. Velocity of sound away from the source

Q. A circular plate of area $0.8{\text{cm}}^2$ is kept at a distance of $2\text{m}$ from a source of sound of power $\pi \text{W}$. Find the amount of energy received by the plate in $4\text{s}$.

1. $50\mu \text{J}$
2. $30\mu \text{J}$
3. $20\mu \text{J}$
4. $15\mu \text{J}$