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Physics : Part-II For Class XI
Waves
for school prepration

Questions keep getting added here on regular intervals. Please do keep checking this section.

(Q.1) What types of waves are sound and light?

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(Q.2) If the temperature increases, then what happens to the frequency of the sound produced by the organ pipe?

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(Q.3) In case of standing wave, where constructive interference is formed?

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(Q.4) Is the phenomena of beats observable in case of two light waves of nearly equal frequencies?

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(Q.5) Will there be a doppler effect if source and listener both move in the same direction with the same speed?

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(Q.6) What are pressure waves?

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(Q.7) Can a stretched string fixed at both ends vibrate simultaneously in more than one mode?

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(Q.8) What is the phase difference between the prongs of a tuning fork?

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(Q.9) Ultrasonic, infrasonic and audible sound travel through a medium with speeds v_u, v_i and v_a respectively, then

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(A) v_i = v_a = v_u
(B) v_u > v₁ > v_i
(C) v_u< v_a < v_i
(D) v_a

v_u = v_i
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(Q.10) If two waves of amplitude a₁ and a₂ produce a resultant wave of amplitude A, then the phase difference between them is

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(A) 60°

Q.11) If in a gramophone, a music record is made to turn faster, the

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(A) intensity increases
(B) pitch increases
(C) timber changes
(D) pitch decreases
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(Q.12) If T is the reverberation time of an auditorium of volume V, then

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(A)

(B)

(C)

(D)

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(Q.13) A wave travelling in positive direction with a = 0.2 m, velocity = 360 m/sec and = 60 m then the correct expression for the wave is

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(A)

(B)

(C)

(D)

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(Q.14) In an orchestra, the musical sounds of different instruments are distinguished from one another by which of the following characteristic?

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(A) Pitch
(B) Loudness
(C) Quality
(D) Overtones
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(Q.15) An open pipe produces fundamental note. All of a sudden one of its ends is closed. If again fundamental note is emitted, the frequency of the note will be

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(A) Double
(B) Half
(C) Same
(D) None of the above
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(Q.16) When two tuning forks A and B are sounded together x beats per second are heard.Frequency of A is n. Now when one prong of fork B is loaded with wax, the number of beats heard per second decreases. The frequency of B is

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(A) n ? x
(B) n + x
(C) n ? 2x
(D) n ? x²
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(Q.17) A man is watching two trains, one leaving and the other coming in with equal speeds of 4 m/sec. If they sound their whistles, each of frequency 240Hz, the number of beats heard by the man (velocity of sound in air = 330 m/s) will be equal to

( 1 mark )

(A) 0
(B) 3
(C) 6
(D) 12
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(Q.18) A source of sound moves towards an observer.

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(A) The amplitude of vibration of the particles is increased.
(B) The wavelength of sound in the medium towards the observer is decreased.
(C) The frequency of the source is increased.
(D) The velocity of the sound in the medium is increased.
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(Q.19) If n₁, n₂ and n₃ are the fundamental frequencies of three segments into which a string in divided, then the original fundamental frequency n of the string is given by

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(A)

(B)

(C)

(D) n = n₁ + n₂ + n₃
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(Q.20) A pipe open at both the ends produces a note of fundamental frequency f₁^. When the pipe is kept with th of its length in water, it produces a note of frequency f₂. The ratio is

( 1 mark )

(A)

(B)

(C) 2
(D)

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(Q.21) The function y = sin² represents

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(A) a simple harmonic motion with a period 2

.
(B) an S.H.M. with a period

.
(C) a periodic motion with period

.
(D) a periodic motion with period

.
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(Q.22) Two sound sources emitting sound each of wavelength are fixed at a given distance apart. A listener moves with a velocity u along the line joining the two sources. The number of beats heard by him per second is

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(A)

(B)

(C)

(D)

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(Q.23) A car is moving towards a cliff. The driver sounds a horn of frequency . The reflected sound heard by the driver has frequency 2. If v is the speed of sound, the speed of the car will be

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(A) v
(B)

(C)

(D)

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(Q.24) The equation of stationary wave along a stretched string is given by cos 40t, where x & y are in cm and t is in seconds. The separation between two adjacent nodes is

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(A) 2.5 cm
(B) 3 cm
(C) 4 cm
(D) 6 cm
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(Q.25) If the tension & diameter of a sonometer wire of fundamental frequency n is doubled and density is halved then its fundamental frequency will become

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(A) n
(B)

(C)

(D) 2 n.
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(Q.26) Two waves represented by the following equations are travelling in the same medium
y₁ = 5 sin 2(75 t ? 0.25x) ; y₂ = 10 sin 2(150 ? 0.50)
The intensity of two waves is

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(A) 2 : 1
(B) 4 : 1
(C) 8 : 1
(D) 16 : 1
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(Q.27) The engine of a train sounds a whistle at frequency . The frequency heard by a passenger is

( 1 mark )

(A)

(B)

(C)

(D)

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(Q.28) A sonometer wire is in unison with a tuning fork. Keeping the same tension the length of the wire between the bridges is doubled. The tuning fork can still be in resonance with the wire provided the wire now vibrates in

( 1 mark )

(A) 2 segments
(B) 3 segments
(C) 4 segments
(D) 6 segments
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(Q.29) The distance between two points differing in phase by 60° on a wave having a wave velocity 360 m/sec and frequency 500 Hz is

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(A) 0.12 m
(B) 0.18 m
(C) 0.36 m
(D) 0.72 m
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(Q.30) The path difference between two waves y₁ = a₁ sin ; y₂ = a₂ cos

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(A)

(B)

(C)

(D)

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(Q.31) An aeroplane passes over a village with a velocity 200 m/sec at a height of 490 m. It blows a whistle of 1 kHz constantly. The frequency change observed by the people of village as it passes over them in one second is

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(A) 238.6 Hz
(B) 268.6 Hz
(C) 236.8 Hz
(D) 266.8 Hz
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(Q.32) In a resonance tube the first resonance occurs at 16 cm and the second resonance occurs at 49 cm. The end correction will be

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(A) 0.3 cm
(B) 0.5 cm
(C) 0.8 cm
(D) 1.0 cm
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(Q.33) A wire has frequency f. Its length is doubled by stretching. Its frequency now will be

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(A) 1.4 f
(B) 0.7 f
(C) 2 f
(D) f
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(Q.34) A wave pulse is traveling on a string of linear mass density 1.0 g/cm under a tension of 1 kg wt. What time taken by the pulse to travel a distance of 50 cm on the string. Take g= 10 m/s²

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(A) 0.05 s
(B) 0.5
(C) 0.12 s
(D) 1 s
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(Q.35) A wave pulse is traveling on a string of linear mass density 1.0 g/cm under a tension of 1 kg wt. What is the time taken by the pulse to travel a distance of 50 cm on the string? Take g= 10 m/s²

( 1 mark )

(A) 0.05 s
(B) 0.5
(C) 0.12 s
(D) 1 s
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(Q.36) Two closed organ pipes of length 50 cm and 51 cm long give 16 beats in 20 sec. When each pipe is sounded in its fundamental mode, what is the velocity of sound?

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(A) 12.4 m/s
(B) 40 m/s
(C) 13.44 m/s
(D) None of these
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(Q.37) A closed organ pipe and an open organ pipe are tuned to the same fundamental frequency. The ratio of their length is

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(A) 1:2
(B) 1:4
(C) 2:1
(D) 1:1
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(Q.38) If the ratio of the amplitudes of the two interfering beams be 2:3 then find the ratio of the minimum and maximum intensities of sound?

( 2 Marks )

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(Q.39) Is the velocity of vibration of the medium same as the velocity of the wave motion?

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(Q.40) The displacement of a wave is represented by y = 0.25X10^-3sin(500t-0.05x) where all the quantities are in their proper units. Find the maximum particle velocity of the medium?

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(Q.41) At what temperature, velocity of sound at 27⁰C doubles?

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(Q.42) A string of mass 2 kg is under a tension of 200 N. The length of the stretched string is 10 m. If the transverse jerk is struck at one end of the string, how long does the disturbance take to reach the other end?

( 2 Marks )

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(Q.43) An open organ pipe has fundamental frequency of 300 Hz. Find the length of the pipe. Speed of sound is 330m/sec.

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(Q.44) What is transferred in a wave from one point to another?

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(Q.45) A wave pulse is traveling on a string of linear mass density 1.0 g/cm under a tension of 1 kg weight. Find the time taken by the pulse to reach a distance of 60 cm on the string.

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(Q.46) The equation of a traveling wave is given by y = 60cos(1800t-6x) where y is in microns, t is in seconds and x is in metres. Find the ratio of maximum particle velocity to the velocity of wave propogation.

( 2 Marks )

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(Q.47) The fundamental frequency of a closed organ pipe is equal to the first overtone frequency of an open organ pipe. If the length of the open pipe is 60 cm, what is the length of the closed pipe?

( 3 Marks )

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(Q.48) Find the molecular weight of a gas in which the velocity of sound is 1260 m/sec at 0⁰C and whose

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(Q.49) Two tuning forks A and B set in vibration gives 4 beats per second. If a prong of the fork A is filed, the beats per second is reduced to 2. Determine the frequency of A if that of B is 250 Hz.

( 3 Marks )

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(Q.50) The extension in the string obeying Hook's law is x. The speed of sound in string is v. If the extension in the string is increased to1.5x then find the speed of sound.

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(Q.51) Tube A has both ends open while tube B has one end closed, otherwise they are identical. Find the ratio of fundamental frequencies of tube A and B.

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(Q.52) What are stationary waves?

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(Q.53) A string is stretched between fixed points separated by 75 cm. It is observed to have resonant frequencies of 420 Hz and 315 Hz. There are no other resonant frequencies between these two. Find the lowest resonant frequency for this string?

( 3 Marks )

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(Q.54) In a sonometer experiment, resonance is obtained when the experimental wire has length 21 cm between the bridges and vibrations are excited by a fork of frequency 256 Hz. If fork of frequency 384 Hz is used, what will be the change in the resonance length?

( 3 Marks )

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(Q.55) Two trains are moving towards each other at speeds of 54 km/hr and 36 km/hr respectively relative to the ground. The first train sounds a whistle of frequency 600 Hz. Find the frequency of the whistle as heard by a passenger in the second train (a) before the trains meet and (b) after the trains have crossed each other. The speed of sound in air is 340m/sec.

( 5 Marks )

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(Q.56) An observer moves towards a stationary source with a velocity 1/5 of the velocity of sound. What is the percentage increase in the apparent frequency?

( 5 Marks )

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(Q.57) The difference between apparent frequencies of a source of sound as perceived by an observer during its approach and recession is 2% of the natural frequency of the source. Find the velocity of the source. Take velocity of sound as 350 m/sec.

( 5 Marks )

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(Q.58) A stationary source emits a sound towards a wall moving towards it with a velocity u. Speed of sound in air is v. Find the fractional change in wavelength of the sound sent and the sound reflected which is observed at source.

( 5 Marks )

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(B) 90°
(C) 120°

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