Reflection of Sound Waves

Q. How many time more intense is 90dB sound than 40dB
ans is 100000

Q.

At a place the speed of sound of frequency 300Hz is V. At the same place the speed of 150 Hz sound will be

Q.

The change in frequency due to Dopplers effect does not depend on

1. The speed of the source

2. The speed of the observer

3. The frequency of the source

4. Separation between the source and the observer

Q.

The amplitude of SHM at resonance is _______ in the ideal case of zero damping.

Q.

Does mirror reflect or absorb sound?

Q. A siren of frequency $f_0$ approaches a stationary observer and then recedes from the observer. If the velocity of source $v_s$ satisfies the condition $(v_s\ll v)$ where $v$ is the velocity of sound, then the apparent change in frequency is:

[Assume, medium is stationary]

1. $\frac{2f_0{v}_s}{v}$
2. $\frac{2f_{0}v}{v_s}$
3. $\frac{f_0}{v}$
4. $\frac{2v{v}_s}{f_0}$

Q.

The driver of a car traveling at a speed of $30\frac{m}{s}$ towards a hill sounds a horn of frequency $600Hz$. If the velocity of sound in air is $330\frac{m}{s}$, the frequency of reflected sound as heard by the driver is then

Q. In Kundt's tube experiment, a metal rod of length $2\text{m}$ and density $8{\text{g/cm}}^3$ clamped at middle gives dust heaps in a Kundt's tube at intervals of $10\text{cm}$. Calculate the Young's modulus of the material of rod. The speed of sound, in the gas is $360\text{m/s}$.

1. $2.12\times {10}^{11}{\text{N/m}}^2$
2. $2.12\times {10}^{10}{\text{N/m}}^2$
3. $4.14\times {10}^{11}{\text{N/m}}^2$
4. $4.14\times {10}^{10}{\text{N/m}}^2$

Q. Match the informations about mechanical waves given in column-I with that given in column-II
$\begin{array}{cc}\text{Column - I}& \text{Column - II}\\ \text{(Nature of wave)}& \text{(Properties)}\\ \text{(A) Transverse progressive wave}& \text{(P) Amplitude of all particles is same.}\\ \text{(B) Longitudinal progressive wave}& \text{(Q) Phase of all the particles may be same.}\\ \text{(C) Transverse standing wave}& \text{(R) May occur in gases.}\\ \text{(D) Longitudinal standing wave}& \text{(S) KE and PE of a small element may be maximum}\end{array}$
Which of the following option has the correct combination considering column-I and column-II ?

Note that any information in column-I may have more than one matching options in column-II.

1. $D\to QS$
2. $C\to R$
3. $B\to PRS$
4. $A\to PR$

Q.

During the rain, we see lightning first and then thunder why?

Q.

Why thunder is always heard after lightning?

Q. A train approaching a crossing $\text{X}$ at a speed $40\text{m/s}$ sounds a horn of frequency $620\text{Hz}$, when it is at a distance of $30\text{m}$ from the crossing. Speed of sound in air is $334\text{m/s}$. What is the frequency heard by an observer (at rest) who is at a perpendicular distance of $40\text{m}$ from the crossing on the straight road.

[Assume, medium is stationary]

1. $620\text{Hz}$
2. $310\text{Hz}$
3. $688\text{Hz}$
4. $668\text{Hz}$

Q. A source of sound and detector are placed at the same place on ground. At t = 0, the source S is projected towards reflector with velocity $V_0$ in vertically upward direction and reflector starts moving down with constant velocity $v_0$. At t = 0, the vertical separation between the reflector and source is $H(>\frac{v_0^2)}{2g})$. The speed of sound in air is $v(\gg v_0)$. Take f_0 as frequency of sound waves emitted by source. Based on above information answer the following questions.

Wavelength of sound waves as received by detector before reflection at $t=\frac{V_0}{2g}$, is

1. $\frac{v+\frac{v_0}{2}}{f_0}$
2. $\frac{v}{f_0}$
3. $\frac{\{v-\frac{v_0}{2}{\}}^2}{v{f}_0}$
4. $\frac{v-\frac{v_0}{2}}{f_0}$

Q. List two applications of reflection of sound.

Q. When a sound wave, travelling in a medium bounces back to the same medium after striking the same second medium then _______ occurs.

1. reflection
2. refraction
3. diffraction
4. scattering

Q. A car is moving towards a hill cliff. The driver sounds a horn of frequency f. The reflected sound heard by the driver has frequency 2f if v the velocity of sound, then the velocity of the car , in units will be.

Q. Which of the following waves is progressing in the $y$ direction ?

1. $x=x_0\cos (\omega t-ky)$
2. $y=y_0\cos (\omega t-kx)$
3. $y=y_0\cos kx\sin \omega t$
4. $y=y_0\sin kx\cos \omega t$

Q. A radar sends a signal to an aircraft at a distance of $30km$ away and receives it back after $2\times {10}^{-4}$ second. What is the speed of the signal?

Q. A sound wave of frequency $f$ horizontal to the right. It is reflected from a large vertical plane surface moving to left with a speed $v$. The speed of sound in medium is $C$

1. The number of wave striking the surface per second is $f\frac{(c+v)}{c}$
2. The wavelength of reflected wave is $\frac{c(c-v)}{f(c+v)}$
3. The frequency of the reflected wave is $f\frac{(c-v)}{(c-v)}$
4. The number of beast heard by a stationary listening to the reflected surface is $\frac{vf}{c-v}$

Q. Sound follow same laws of reflection as light does?

1. True
2. False

Q. Amplitude of vibration of any particle in a standing wave produced along a stretched string depends on

1. frequency of incident wave
2. time of reflected wave
3. location of the particle
4. time

Q.

A train of sound waves is propagated along an organ pipe and gets reflected from an open end. If the displacement amplitude of the waves (incident and reflected) are 0.002 cm for both of them, the frequency is 100 Hz and wavelength is 40 cm, then the displacement amplitude of vibration at a point at a distance 10 cm from the open end is,

1. 0.002 cm
2. 0.003 cm
3. 0.001 cm
4. 0.000 cm

Q. The stethoscope used by doctors works on the principle of

1. Refraction of sound
2. Reflection of sound
3. Interference of sound
4. Absorption of sound

Q. If the tension in the string is increased by $5kgwt$ the frequency of the fundamental tone increases in the ratio $2:3$. What was the initial tension in the string?

Q. Soundproof walls use materials that

1. reflects sound in all directions
2. absorbs sound
3. reflects sound in only one direction
4. amplify sound waves on one side and weaken sound waves on other

Q. Fill in the blank.

1. reflection
2. diffraction
3. refraction
4. scattering

Q. If we put a cardboard (say 20 cm x 20 cm) between a light source and our eyes, we can't see the light. But when we put the same cardboard between a sound source and our ear, we hear the sound almost clearly. Explain.

Q. A plane sound wave traveling with velocity 'v' in a medium A reaches a point on the interface of medium A and medium B. If velocity of sound in medium B is $2v$, the angle of incidence for total internal reflection of the wave will be greater than ($\sin {30}^o=0.5$ and $\sin {90}^o=1$).

1. ${30}^o$
2. ${15}^o$
3. ${90}^o$
4. ${45}^o$

Q.

A train of sound waves is propagated along an organ pipe and gets reflected from an open end. If the displacement amplitude of the waves (incident and reflected) are 0.002 cm, the frequency is 1000 Hz and wavelength is 40 cm, then the displacement amplitude of vibration at a point at distance 10 cm from the open end inside the pipe, is

1. 0.002 cm

2. 0.003 cm

3. 0.001 cm

4. 0.000 cm

Q. Megaphone works on the principle of reflection of sound.

1. True
2. False