427 + Interview Questions in WAVES IN GENERAL AWARENESS Page 3 InterviewSolution

101.	A transverse harmonic wave on a string is described by y(x,t) = 3.0 sin (36t + 0.018x + π/4) where x and y are in cm. and t in s. The positive direction of x is from left to right.(a) Is this a travelling wave or a stationary wave? If it is a travelling, what are the speed and direction of its propagation?(b) What are its amplitude and frequency?(c) What is the initial phase at the origin?(d) What is the least distance between two successive crests in the wave?
Answer» (a) It is travelling wave which is propagating from right to left. Comparing the given equation with, y(x,t) = γ sin(ωt + kx + ϕ) we get γ = 3 cm ω = 36 rad s^-1 k = 2π/λ = 0.018 cm^-1 and ϕ = π/4 The speed of the wave, v = λv = {2πv}/{2π/λ} = ω/k = 36/0.018 = 2000 cm s^-1 = 20 ms^-1 (b) Amplitude of the wave, γ = 3 cm and frequency, v = ω/2π = {36}/{2 x 3.14} = 5.73 Hz (c) Initial phase ϕ = π/4 rad (d) Least distance between two successive crest = wavelength = λ = 2π/k = {2 x 3.14}/{0.018} cm = 3.49 x 10² cm = 3.49 m

101.

A transverse harmonic wave on a string is described by y(x,t) = 3.0 sin (36t + 0.018x + π/4) where x and y are in cm. and t in s. The positive direction of x is from left to right.(a) Is this a travelling wave or a stationary wave? If it is a travelling, what are the speed and direction of its propagation?(b) What are its amplitude and frequency?(c) What is the initial phase at the origin?(d) What is the least distance between two successive crests in the wave?

Answer»

(a) It is travelling wave which is propagating from right to left. Comparing the given equation with,

y(x,t) = γ sin(ωt + kx + ϕ)

we get γ = 3 cm

ω = 36 rad s^-1

k = 2π/λ = 0.018 cm^-1

and ϕ = π/4

The speed of the wave,

v = λv = {2πv}/{2π/λ} = ω/k = 36/0.018 = 2000 cm s^-1

= 20 ms^-1

(b) Amplitude of the wave,

γ = 3 cm

and frequency, v = ω/2π = {36}/{2 x 3.14} = 5.73 Hz

(c) Initial phase

ϕ = π/4 rad

(d) Least distance between two successive crest = wavelength

= λ = 2π/k = {2 x 3.14}/{0.018} cm = 3.49 x 10² cm = 3.49 m

Discussion

102.	A transverse wave propagating along x-axis is represented by: `y(x,t)=8.0sin(0.5pix-4pit-(pi)/(4))` Where `x` is in metres and `t` is in seconds. The speed of the wave is:A. `4pi m//s`B. `0.5pi m//s`C. `pi/4 m//s`D. 8 m/s
Answer» Correct Answer - d

Discussion

103.	A transverse wave propagating on a stretched string of linear density 3 × 10-4 kg m-1 is represented by the equation, y = 0.2 sin (1.5x + 60t)Where x is in metres and t is in seconds. The tension in the string (in newtons) is:(a) 0.24(b) 0.48 (c) 1.20 (d) 1.80
Answer» (a) 0.48 v = \(\sqrt{\frac{T}{m}}\) = \(\frac{ω}{k}\) ⇒ T = (\(\frac{ω}{k}\))² m = \((\frac{60}{1.5})^2\) x 3 x 10^-⁴ = 0.48 N

103.

A transverse wave propagating on a stretched string of linear density 3 × 10-4 kg m-1 is represented by the equation, y = 0.2 sin (1.5x + 60t)Where x is in metres and t is in seconds. The tension in the string (in newtons) is:(a) 0.24(b) 0.48 (c) 1.20 (d) 1.80

Answer»

(a) 0.48

v = \(\sqrt{\frac{T}{m}}\) = \(\frac{ω}{k}\)

⇒ T = (\(\frac{ω}{k}\))² m = \((\frac{60}{1.5})^2\) x 3 x 10^-⁴

= 0.48 N

Discussion

104.	A pulse of a wave train travel s along a stretched string and reaches the fixed end of the string and reaches the fixed end of the string.it will be reflected back withA. a phase change of `180^(@)` with velocity reversedB. the same phase as the incident pulse with no reversal of velocityC. a phase change of `180^(@)` with no reveral of velocityD. the same phase as the incident pulse but with velocity reversed
Answer» Correct Answer - a

Discussion

105.	A string is stretched between fixed points separated by `75.0cm`. It is observed to have resonant frequencies of `420 Hz` and `315 Hz`. There are no other resonant frequencies between these two. Then, the lowest resonant frequency for this string isA. (a) `105 Hz`B. (b) `1.05 Hz`C. ( c ) `1050 Hz`D. (d) `10.5 Hz`
Answer» Correct Answer - A (a) Given `(nv)/(2l) = 315` and `(n + 1)(v)/(2l) = 420` rArr `(n + 1)/(n) = (420)/(315)` rArr `n = 3` Hence `3 xx (v)/(2l) = 315` rArr `(v)/(2l) = 105 Hz` lowest resonant frequency is when `n = 1` Therefore lowest resonant frequency `= 105 Hz`.

Discussion

106.	A uniform rope of length `12m` and mass `6kg` hangs vertically from a rigid support. A block of mass `2kg` is attached to the free end of the rope. A transverse pulse of wavelength `0.06m` is produced at the lower end of the rope. What is the wavelength of the pulse whwn it reaches the top of the rope?
Answer» KEY CONCEPT : The velocity of wave on the string is given by the formula `v = sqrt((T)/(m))` where `T` is the tension and `m` is the mass per unit length. Since the tension in the string will increase as we move up the string (as the string has mass), therefore the velocity of wave will also increse. (`m` is the same as the rope is uniform) :. `(v_(1))/(v_(2)) = sqrt((T_(1))/(T_(2))) = sqrt((2 xx 9.8)/(8 xx 9.8)) = (1)/(2)` :. `v_(2) = 2v_(1)` Since frequency remains the same :. `lambda_(2) = 2lambda_(1) = 2 xx 0.06 = 0.12m`

Discussion

107.	In a stationary wave, all particles of the medium cross the mean position with (A. different speeds at different instantsB. different speeds at the same instantC. same speed at different instantD. same speed at the same instant
Answer» Correct Answer - B

Discussion

108.	Two vibrating tuning forks producing waves given by `y_(1) = 27 "sin" 600 pi t "and" y_(2) = 27 "sin" 604 pi t` are held near the ear of a person, how many beats will be heard in three seconds by him ?A. 4B. 2C. 6D. 12
Answer» Correct Answer - C

Discussion

109.	A wave disturbance in a medium is described by `y(x, t) = 0.02 cos((50pit + (pi)/(2))cos(10pix)` where `x and y` are in meter and `t` is in second`A. (a) A node occurs at `x = 0.15 m`B. (b) A antinode occurs at `x = 0.3 m`C. ( c ) A speed wave is `5 ms^(-1)`D. (d) A wave lengthis `0.3 m`
Answer» Correct Answer - C ( c ) Comaring it with `y(x, t) = A cos(omegat + pi//2)coos k x` If `k x = pi//2`, a node occurs, :. `10pi x = pi//2 rArr x = 0.05m` If `k x = pi`,an antinode occurs rArr `10pix = pi rArr x = 0.1m` aAlso speed of wave `= (omega)/(k) = (50)/(10pi) = 5m//s` and `lambda = 2pi//k = 2pi//10pi = 0.2m`

Discussion

110.	The velocity of sound waves in air is `330m//s`. For a particluar sound in air, a path difference of `40 cm` is equivalent to a phase difference of `1.6pi`. The frequency of this wave isA. 165 HzB. 150 HzC. 660 HzD. 330 Hz
Answer» Correct Answer - c

Discussion

111.	There are 26 tuning forks arranged in the decreasing order of their frequencies. Each tuning fork gives 3 beats with the next. The first one is octave of the last. What is the frequency of 18th tuning fork ?A. 100 HzB. 99 HzC. 96 HzD. 103 Hz
Answer» Correct Answer - B Let the frequency of first tuning fork is `upsilon`. The frequencies of other tuning forks are `(upsilon-3),(upsilon-2xx3),â€¦.,(upsilon-17xx3),â€¦(upsilon-25xx3).` As per given condition, `upsilon=2(upsilon-25xx3)orupsilon=2upsilon-25xx6` `orupsilon=25xx6=150Hz` The frequency of the `18^(th)` tuning fork `=upsilon-17xx3=150-51=99 Hz`

Discussion

112.	A source of sound `S` emitting waves of frequency `100 Hz` and an observer `O` are located at some distance from each other. The source is moving with a speed of `19.4ms^-1` at an angle of `60^(@)` with the source observer line as shown in the figure. The observer is at rest. The apparent frequency observed by the observer (velocity of sound in air `330ms^-1`) isA. 100 HzB. 103HzC. 106 HzD. 97 Hz
Answer» Correct Answer - b

Discussion

113.	Two open organs pipes of fundamental frequencies `v_(1)` and `v_(2)` are joined in series. The fundamental frequency of the new pipe so obtained will beA. `upsilon_(1)+upsilon_(2)`B. `(upsilon_(1)upsilon_(2))/((upsilon_(1)+upsilon_(2))`C. `(upsilon_(1)upsilon_(2))/(upsilon_(1)+upsilon_(2)`D. `sqrt((upsilon_(1)^(2)+upsilon_(2)^(2)))`
Answer» Correct Answer - B `upsilon_(1)=v/(2L_(1))`..(i) `upsilon_(2)=v/(2L_(2))`â€¦(ii) When two pipes are joined in series, the fundamental frequency of the new pipe is `upsilon=v/(2(L_(1)+L_(2))=v/(2L_(1)+2L_(2))` `=v/(v/(upsilon_(1))+v/(upsilon_(2)))` 0=(Using (i) and (ii)) `=(upsilon_(1)upsilon_(2))/(upsilon_(2)+upsilon_(1))`

Discussion

114.	Which of the following wave does not travel in vaccum ?A. Seismic wavesB. X-raysC. LightD. Radio waves
Answer» Correct Answer - A Light, X-rays and radio waves are electro-magnetic waves. They do not require medium for their propagation. They can travel through vacuum, Seismic waves are mechanical waves. They require medium for their propagation. They do not travel in vacuum.

Discussion

115.	In a transverse wave, the particles of the mediumA. vibrate in a direction perpendicular to the direction of the propagation.B. vibrate in a direction parallel to the direction or of the propagationC. move in circleD. move in ellipse
Answer» Correct Answer - A In a transverse wave, the particles of the medium vibrate in a direction perpendicular to the direction of the propagation.

Discussion

116.	A medium radio waveband lies between two wavelength 100m and 1000m. Determine the corresponding frequency range (Take velocity of the wave to be 299.8 x 106 m\s).
Answer» We know that, v = \(\nu\lambda\) \(\nu\) = \(\frac{v}{\Delta\lambda}\) \(\nu\) = \(\frac{299.8\times10^6}{1000-100}\) \(\nu\) = \(\frac{299.8\times10^6}{900}\) \(\nu\) = 0.33 x 10⁶ Hz

116.

A medium radio waveband lies between two wavelength 100m and 1000m. Determine the corresponding frequency range (Take velocity of the wave to be 299.8 x 106 m\s).

Answer»

We know that,

v = \(\nu\lambda\)

\(\nu\) = \(\frac{v}{\Delta\lambda}\)

\(\nu\) = \(\frac{299.8\times10^6}{1000-100}\)

\(\nu\) = \(\frac{299.8\times10^6}{900}\)

\(\nu\) = 0.33 x 10⁶ Hz

Discussion

117.	A tuning fork A, marked 512 Hz, produces 5 beats per second, when sounded with another unmarked tuning fork B. If B is loaded with wax, the number of beats is again 5 per second. What is the frequency of tuning fork B when not loaded?A. 502 HzB. 507 HzC. 517 HzD. 522 Hz
Answer» Correct Answer - C

Discussion

118.	A man fires a gun while standing between two parallel hills. If he hears the first echo after 2 s and the second echo 3 s after the first echo, then calculate the distance between the hills the velocity of sound is 330 m/s.
Answer» Correct Answer - 1155m

Discussion

119.	Calculate the speed of longitudinal sound wave in a liquid. The bulk modulus for the liquid is `20xx10^(9)N//m^(2)` and its density is `9.5xx10^(3)kg//m^(3)`.
Answer» Correct Answer - 1450 m/s

Discussion

120.	If the speed of longitudinal mechanical waves in water is `1400m//s` then calculate the bulk modulus of elasticity of water. (given density of water is `1g//cm^(3)`)
Answer» Speed of longitudinal wave is `v=sqrt((B)/(rho))` `140000cm//s=sqrt((B)/(1))` `impliesB=1.96xx10^(10)"dyne"//cm^(2)` `=1.96xx10^(9)N//m^(2)`

Discussion

121.	For aluminium the bulk modulus and modulus of rigidity are `7.5xx10^(10) Nm^(-2)`. Find the velocity of longitudinal waves in the mediu. Density of aluminium is `2.7xx10^(3) kgm^(3)`.
Answer» We are given `B=7.5xx10^(10)N//m^(2)` `rho=2.70xx10^(3)kg//m^(3)` `v=sqrt((B)/(rho))=sqrt((75xx10^(9))/(2.70xx10^(3)))` `=10^(3)sqrt((75)/(2.7))=10^(3)sqrt((75)/(2.7))` `=10^(3)xx5.27` `v=5.27xx10^(3)m//s`

Discussion

122.	You have learnt that a travelling wave in one dimension is represented by a function y = f (x, t) where x and t must appear in the combination x – v t or x + vt, i.e., y = f (x ± v t). Is the converse true? Examine if the following functions for y can possibly represent a travelling wave :(a) (x – vt)2(b) log [(x + Vy)/x0](c) 1/(x + vt)
Answer» The converse is not true. For any function to represent a travelling wave, an obvious requirement is that the function should be finite at all times and finite everywhere. Function a) and b) do not satisfy this requirement and hence cannot represent a travelling wave. Only function c) satisfies the condition.

122.

You have learnt that a travelling wave in one dimension is represented by a function y = f (x, t) where x and t must appear in the combination x – v t or x + vt, i.e., y = f (x ± v t). Is the converse true? Examine if the following functions for y can possibly represent a travelling wave :(a) (x – vt)2(b) log [(x + Vy)/x0](c) 1/(x + vt)

Answer»

The converse is not true. For any function to represent a travelling wave, an obvious requirement is that the function should be finite at all times and finite everywhere.

Function a) and b) do not satisfy this requirement and hence cannot represent a travelling wave. Only function c) satisfies the condition.

Discussion

123.	You have learnt that a travelling wave in one dimension is represented by a function `y = f( x,t ) ` where x and t must appear in the combination `x -vt ` or ` x + vt `, i.e., `y = f( x+- v t )`. Is the converse true ? Examine if the following function for y can possibly represent a travelling wave `:` (a) ` (x - vt ) 2` (b) ` log[ ( x+ vt ) //x_(0)]` (c ) ` 1//(x+vt )`
Answer» No, the converse is not true. The basic requirement for a wave function to represent a travelling wave is that for all value of x& t, wave function must have a finite value . Out of the given function y, no one satisfies this condition therefore, none can represent a travelling wave.

Discussion

124.	Two progressive transverse waves given by `y_(1) =0.007 sinpi ( 12x- 500 t )`and `y _(2) = 0.07 sin pi ( 12x+500t)` travelling along a stretched string from nodes and antinodes . What is the displacement at the (a) nodes (b) antinodes ? What is the wavelength of the standing wave ?
Answer» `A_(1) = 0.07 ,A_(2) = 0.07 , K = 12pi ` (a) At nodes , displacement `y= A_(1) -A_(2) = 0.07-0.07 =0` (b) At antinodes ,displacement `y =A_(1) + A_(2) = 0.07 +0.07 =0.14m` (c ) Wavelength `lambda = ( 2pi)/( K ) = (2pi)/(12pi) = 0.16m`

Discussion

125.	Two cars moving in opposite directions approach each other with speed of 22 ms-1 and 16.5 ms-1 respectively. The driver of the first car blows a horn having a frequency 400 Hz. To find the frequency heard by the driver of the second car
Answer» \(f_A = f[\frac{v + v_0}{v - v_s}]\) = 400 \([\frac{340 + 16.5}{340 - 22}]\) = 400\([\frac{356.5}{318}]\) = 400 x 1.1210 \(f_A = 448.4 Hz\)

125.

Two cars moving in opposite directions approach each other with speed of 22 ms-1 and 16.5 ms-1 respectively. The driver of the first car blows a horn having a frequency 400 Hz. To find the frequency heard by the driver of the second car

Answer»

\(f_A = f[\frac{v + v_0}{v - v_s}]\) = 400 \([\frac{340 + 16.5}{340 - 22}]\)

= 400\([\frac{356.5}{318}]\) = 400 x 1.1210

\(f_A = 448.4 Hz\)

Discussion

126.	A string is stretched between two rigit supports.What frequencies of vibration are possible in such a string ?
Answer» The possible frequencies of vibration in a stretched string between two rigid supports is given by `v_(n) =(n+(1)/2)(v)/(2l)`where n = 0,1,2,3,....

Discussion

127.	A source of ultrasonic wave is emitting ultrasonic waves of frequency 30 kHz. It is placed in a moving car. With what velocity is the car moving If the frequency appears to be 20 kHz to a stationary observer? Velocity of sound in car 340 ms-1.
Answer» Here the listener is at rest and the source is moving. As the apparent frequency is lesser than the actual frequency, the source is moving away from the listener. To find the velocity with the source is moving: The apparent frequency is given by, Here,f' is the apparent frequency = 20 kHz f is the actual frequency = 30 kHz v is the velocity of sound = 340 ms^-1 On substituting the values, \(\frac{20}{30}\)= \(\frac{340}{340 + v_s}\) cross multiplying, 2(340 + v_S) = 3 × 340 2 × 340 + 2v_s = 3 × 340 2 . v_s = 3 × 340 – (2 × 340) or 2 . v_s = 340 v_s = \(\frac{340}{2}\) = 170ms^-1 ∴ The car is moving with a velocity of 170ms^-1 away from the listener.

127.

A source of ultrasonic wave is emitting ultrasonic waves of frequency 30 kHz. It is placed in a moving car. With what velocity is the car moving If the frequency appears to be 20 kHz to a stationary observer? Velocity of sound in car 340 ms-1.

Answer»

Here the listener is at rest and the source is moving. As the apparent frequency is lesser than the actual frequency, the source is moving away from the listener.

To find the velocity with the source is moving:

The apparent frequency is given by,

Here,f' is the apparent frequency = 20 kHz

f is the actual frequency = 30 kHz

v is the velocity of sound = 340 ms^-1

On substituting the values, \(\frac{20}{30}\)= \(\frac{340}{340 + v_s}\)

cross multiplying, 2(340 + v_S) = 3 × 340 2 × 340 + 2v_s = 3 × 340

2 . v_s = 3 × 340 – (2 × 340) or 2 . v_s = 340

v_s = \(\frac{340}{2}\) = 170ms^-1

∴ The car is moving with a velocity of 170ms^-1 away from the listener.

Discussion

128.	State the factors in which the speed of a wave travelling along a stretched Ideal string depends.
Answer» Tension and mass per unit length.

Discussion

129.	The fundamental frequency of oscillation of a closed pipe is 400 Hs. What will be the fundamental frequency of oscillation of open pipe of the same length?
Answer» f_e = v/4l = 400 Hz f_o = v/2l ⇒ f_o = f_e = 800 Hz.

129.

The fundamental frequency of oscillation of a closed pipe is 400 Hs. What will be the fundamental frequency of oscillation of open pipe of the same length?

Answer»

f_e = v/4l = 400 Hz

f_o = v/2l ⇒ f_o = f_e = 800 Hz.

Discussion

130.	Why is it difficult some times to recognise your friend’s voice on phone?
Answer» Because of modulation.

Discussion

131.	mechanical waves transfer____from one place to the other.A. energyB. matterC. both energy and matterD. neither energy nor matter
Answer» Correct Answer - A

Discussion

132.	Is it possible to have longitudinal waves on a string? A transverse wave in a steel rod?
Answer» No, because string is not stretchable. It can neither be compressed nor rarefied. But transverse waves are possible in a steel rod, because steel has elasticity of shape.

Discussion

133.	The types of mechanical wave we expect the exist in vacuum isA. longitudnal waveB. transverse waveC. Transverse or longitudinal or both (separtely)D. no wave
Answer» Correct Answer - D

Discussion

134.	A flute has several holes in it. Why?
Answer» A flute is an open organ pipe and length of air column can be changed by putting fingers on them and different frequencies can be produced.

Discussion

135.	What is the distance between the two points which have a phase difference of 2π?
Answer» The distance between the two points which have a phase difference of 2π is wavelength.

Discussion

136.	Standing waves can be producedA. (a) on a string clamped at both the ends.B. (b) on a string clamped at one end free at the other.C. ( c ) when incident wave gets reflected from a wallD. (d) when two identical waves with a phase difference of `pi` are moving in the same direction
Answer» Correct Answer - A::B::C (a,b,c) Standing waves are produced by two similar waves superposing while travelling in opposite direction. This can happrn in case (a), (b) and(c ).

Discussion

137.	As a wave propagates,A. (a) the wave intensity remains constant for a sine waveB. (b) the wave intensity decreases as the inverse of the distance from the source for a spherical waveC. (c ) the wave intensity decreases as the inverse square of the distance from the source for a spherical waveD. (d) total intensity of the spherical wave over the spherical surface centered at the source remains constant at all times.
Answer» Correct Answer - A::C::D (a,c,d) For a plane wave, intensity (energy crossing per unit area per unit time) is constant at all points. But for a spherical wave, intensity at a distance `r` from a point source of power `(P)`, is given by `I = (P)/(4pir^(2))` rArr `I prop (1)/(r^(2))` But the total intensity of the spherical wave over the spherical surface centered at the source remains constant at all times.

Discussion

138.	A wave is described by `y=Asin(omega-kx)`. The speeds of which of the following particles in the medium are increasing at time t=0?A. `x=0`B. `x=(pi)/(4k)`C. `x=(pi)/(2k)`D. `x=(3pi)/(4k)`
Answer» Correct Answer - B::C

Discussion

139.	As a wave propagatesA. the wave intensity remains constant for a plane waveB. the wave intensity decreases with the inverse of the distance from the source for a speherical waveC. The wave intensity decreases as the inverse of the square of the distance from the source for a spherical waveD. the total energy of the spherical wave incident over any spherical surface centred at the source remains constant at all times.
Answer» Correct Answer - A::C::D

Discussion

140.	The equation of wave, giving the displacement y is given by `y=10^(-3)sin(120t=3x)` Where, x and y are in metre and t is in second. This equation represents a wave.A. Travelling with a velocity of `40ms^(-1)`B. Or wavelength `(2pi)/(3)m`C. of frequency `(60)/(pi)Hz`D. of amplitude `10^(-3)m`, travelling along negative x direction
Answer» Correct Answer - A::B::C::D

Discussion

141.	The velocity of sound in air is `340ms^(-1)`. A pipe closed at one end has a length of 170 cm. neglecting the end correction, the frquencies at which the pipe can resonate areA. 50 HzB. 100 HzC. 150 hzD. 200 Hz
Answer» Correct Answer - A::C

Discussion

142.	Two waves of frequencies 50 Hz and 45 Hz are produced simultaneously, then the time interval between successive maxima of the resulting wave is [maxima refers to the maximum intensity]A. 0.2 sB. 0.02 sC. 0.04 sD. 0.4 s
Answer» Correct Answer - A

Discussion

143.	if the first overtone of a closed pipe of length 50 cm has the same frequency as the first overtone of an open pipe, then the length of the open pipe isA. 100 cmB. 200 cmC. 66.6 cmD. 33.3 cm
Answer» Correct Answer - C

Discussion

144.	In a wave motion `y = a sin (kx - omegat)`, `y` can representA. (a) electric fieldB. ( b ) magnetic fieldC. ( c ) displacementD. (d) pressure
Answer» Correct Answer - A::B::C::D (a,b,c,d) in the wave motion `y = a(kx - omegat)`, `y` can represent electric and magnetic fields in electromagnetic waves and displacement and pressure in sound waves.

Discussion

145.	A sinusoidal wave is given by y=A sin (kx-`omegat`). The ratio of its maximum particle velocity to wave velocity isA. 1B. `omega`C. `omegaA`D. `kA`
Answer» Correct Answer - D

Discussion

146.	The displacement of an elastic wave is given by the function `y=3 sin omega t +4 cos omegat .` where y is in cm and t is in second. Calculate the resultant amplitude.A. 3 cmB. 4 cmC. 5 cmD. 7 cm
Answer» Correct Answer - C Resultant amplitude=`sqrt(3^(2)+4^(2))=sqrt(9+16)=5 cm`

Discussion

147.	Newton assumed that sound propagation in a gas takes underA. isothemal conditionB. adiabatic conditionC. isobaric conditionD. isentropic condition
Answer» Correct Answer - A Newton assumed that sound propagation in a gas takes under isothermal condition.

Discussion

148.	A sound wave of frequency `f` travels horizontally to the right. It is reflected from a large vertical plane surface moving to left with a speed `v`. The speed of sound in mwdium is `C`A. (a) The number of wave strinking the surface per second is `f((c + v)/(c ))`B. (b) The wavelength of reflected wave is `(c(c-v))/(f(c+v))`C. ( c ) The frequency of the reflected wave is `f(((c+v))/((c-v)))`D. (d) The number of beats heard by a stationary listener to the left if the reflecting surface is `(vf)/(c-v)`
Answer» Correct Answer - A::B::C (a,b,c) Frequency of reflected wave is `f" = f((c + c)/(c - v))` rArr Beat freq. `= f" - f = (2v)/(c - 1)`. Wavelength of reflacted wave = ( c )/(f") =(c(c - v))/(f( c + v))`

Discussion

149.	A sound wave of frequency `f` travels horizontally 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`A. Thee number of wave striking the surface per second is `f((v+c))/(c)`B. the wavelength of reflected wave is `(c(c-v))/(f(c+v))`C. The frequency of reflected wave is `(f(c+v))/(c-v)`D. The number of beats heard by a stationary listener to the left of the reflecting surface is `(vf)/(c-v)`
Answer» Correct Answer - A::B::C

Discussion

150.	Sound of maximum intensity is heard successively at an interval of 0.2 second on sounding two tuning fork to gather. What is the difference of frequencies of two tuning forks?
Answer» The beat period is 0.2 second so that the beat frequency is fb = 1/0.2 = 5HZ. Therefore, the difference of frequencies of the two tuning forks is 5HZ.

150.

Sound of maximum intensity is heard successively at an interval of 0.2 second on sounding two tuning fork to gather. What is the difference of frequencies of two tuning forks?

Answer»

The beat period is 0.2 second so that the beat frequency is fb = 1/0.2 = 5HZ.

Therefore, the difference of frequencies of the two tuning forks is 5HZ.

Discussion

Explore topic-wise InterviewSolutions in .

A transverse wave propagating along x-axis is represented by: `y(x,t)=8.0sin(0.5pix-4pit-(pi)/(4))` Where `x` is in metres and `t` is in seconds. The speed of the wave is:A. `4pi m//s`B. `0.5pi m//s`C. `pi/4 m//s`D. 8 m/s

A transverse wave propagating on a stretched string of linear density 3 × 10-4 kg m-1 is represented by the equation, y = 0.2 sin (1.5x + 60t)Where x is in metres and t is in seconds. The tension in the string (in newtons) is:(a) 0.24(b) 0.48 (c) 1.20 (d) 1.80

In a stationary wave, all particles of the medium cross the mean position with (A. different speeds at different instantsB. different speeds at the same instantC. same speed at different instantD. same speed at the same instant

Two vibrating tuning forks producing waves given by `y_(1) = 27 "sin" 600 pi t "and" y_(2) = 27 "sin" 604 pi t` are held near the ear of a person, how many beats will be heard in three seconds by him ?A. 4B. 2C. 6D. 12

A wave disturbance in a medium is described by `y(x, t) = 0.02 cos((50pit + (pi)/(2))cos(10pix)` where `x and y` are in meter and `t` is in second`A. (a) A node occurs at `x = 0.15 m`B. (b) A antinode occurs at `x = 0.3 m`C. ( c ) A speed wave is `5 ms^(-1)`D. (d) A wave lengthis `0.3 m`

The velocity of sound waves in air is `330m//s`. For a particluar sound in air, a path difference of `40 cm` is equivalent to a phase difference of `1.6pi`. The frequency of this wave isA. 165 HzB. 150 HzC. 660 HzD. 330 Hz

There are 26 tuning forks arranged in the decreasing order of their frequencies. Each tuning fork gives 3 beats with the next. The first one is octave of the last. What is the frequency of 18th tuning fork ?A. 100 HzB. 99 HzC. 96 HzD. 103 Hz

Which of the following wave does not travel in vaccum ?A. Seismic wavesB. X-raysC. LightD. Radio waves

In a transverse wave, the particles of the mediumA. vibrate in a direction perpendicular to the direction of the propagation.B. vibrate in a direction parallel to the direction or of the propagationC. move in circleD. move in ellipse

A medium radio waveband lies between two wavelength 100m and 1000m. Determine the corresponding frequency range (Take velocity of the wave to be 299.8 x 106 m\s).

A tuning fork A, marked 512 Hz, produces 5 beats per second, when sounded with another unmarked tuning fork B. If B is loaded with wax, the number of beats is again 5 per second. What is the frequency of tuning fork B when not loaded?A. 502 HzB. 507 HzC. 517 HzD. 522 Hz

A man fires a gun while standing between two parallel hills. If he hears the first echo after 2 s and the second echo 3 s after the first echo, then calculate the distance between the hills the velocity of sound is 330 m/s.

Calculate the speed of longitudinal sound wave in a liquid. The bulk modulus for the liquid is `20xx10^(9)N//m^(2)` and its density is `9.5xx10^(3)kg//m^(3)`.

If the speed of longitudinal mechanical waves in water is `1400m//s` then calculate the bulk modulus of elasticity of water. (given density of water is `1g//cm^(3)`)

For aluminium the bulk modulus and modulus of rigidity are `7.5xx10^(10) Nm^(-2)`. Find the velocity of longitudinal waves in the mediu. Density of aluminium is `2.7xx10^(3) kgm^(3)`.

Two progressive transverse waves given by `y_(1) =0.007 sinpi ( 12x- 500 t )`and `y _(2) = 0.07 sin pi ( 12x+500t)` travelling along a stretched string from nodes and antinodes . What is the displacement at the (a) nodes (b) antinodes ? What is the wavelength of the standing wave ?

Two cars moving in opposite directions approach each other with speed of 22 ms-1 and 16.5 ms-1 respectively. The driver of the first car blows a horn having a frequency 400 Hz. To find the frequency heard by the driver of the second car

A string is stretched between two rigit supports.What frequencies of vibration are possible in such a string ?

A source of ultrasonic wave is emitting ultrasonic waves of frequency 30 kHz. It is placed in a moving car. With what velocity is the car moving If the frequency appears to be 20 kHz to a stationary observer? Velocity of sound in car 340 ms-1.

State the factors in which the speed of a wave travelling along a stretched Ideal string depends.

The fundamental frequency of oscillation of a closed pipe is 400 Hs. What will be the fundamental frequency of oscillation of open pipe of the same length?

Why is it difficult some times to recognise your friend’s voice on phone?

mechanical waves transfer____from one place to the other.A. energyB. matterC. both energy and matterD. neither energy nor matter

Is it possible to have longitudinal waves on a string? A transverse wave in a steel rod?

The types of mechanical wave we expect the exist in vacuum isA. longitudnal waveB. transverse waveC. Transverse or longitudinal or both (separtely)D. no wave

A flute has several holes in it. Why?

What is the distance between the two points which have a phase difference of 2π?

Standing waves can be producedA. (a) on a string clamped at both the ends.B. (b) on a string clamped at one end free at the other.C. ( c ) when incident wave gets reflected from a wallD. (d) when two identical waves with a phase difference of `pi` are moving in the same direction

A wave is described by `y=Asin(omega-kx)`. The speeds of which of the following particles in the medium are increasing at time t=0?A. `x=0`B. `x=(pi)/(4k)`C. `x=(pi)/(2k)`D. `x=(3pi)/(4k)`

The velocity of sound in air is `340ms^(-1)`. A pipe closed at one end has a length of 170 cm. neglecting the end correction, the frquencies at which the pipe can resonate areA. 50 HzB. 100 HzC. 150 hzD. 200 Hz

Two waves of frequencies 50 Hz and 45 Hz are produced simultaneously, then the time interval between successive maxima of the resulting wave is [maxima refers to the maximum intensity]A. 0.2 sB. 0.02 sC. 0.04 sD. 0.4 s

if the first overtone of a closed pipe of length 50 cm has the same frequency as the first overtone of an open pipe, then the length of the open pipe isA. 100 cmB. 200 cmC. 66.6 cmD. 33.3 cm

In a wave motion `y = a sin (kx - omegat)`, `y` can representA. (a) electric fieldB. ( b ) magnetic fieldC. ( c ) displacementD. (d) pressure

A sinusoidal wave is given by y=A sin (kx-`omegat`). The ratio of its maximum particle velocity to wave velocity isA. 1B. `omega`C. `omegaA`D. `kA`

The displacement of an elastic wave is given by the function `y=3 sin omega t +4 cos omegat .` where y is in cm and t is in second. Calculate the resultant amplitude.A. 3 cmB. 4 cmC. 5 cmD. 7 cm

Newton assumed that sound propagation in a gas takes underA. isothemal conditionB. adiabatic conditionC. isobaric conditionD. isentropic condition

Sound of maximum intensity is heard successively at an interval of 0.2 second on sounding two tuning fork to gather. What is the difference of frequencies of two tuning forks?