Chapter 7 Sound and Vibrations – Solved MCQs (Class 11 Physics)

Q1. The principle of superposition in waves is stated as:

A) The displacement of a wave is the sum of the displacements of its individual components
B) The velocity of a wave is the product of its individual components
C) The frequency of a wave is the difference of its individual components
D) The amplitude of a wave is the ratio of its individual components

✅ Correct Answer: A

Explanation:
According to the principle of superposition, when waves overlap, the resultant displacement at any point is the algebraic sum of individual displacements.

Q2. The principle of superposition of waves states that when two or more waves overlap, the resultant displacement is:

A) The product of individual displacements
B) The sum of individual displacements
C) The difference between the largest and the smallest displacements
D) Always zero

✅ Correct Answer: B

Explanation:
Overlapping waves add their displacements point by point, giving a resultant displacement equal to their sum.

Q3. The superposition principle applies to:

A) Only mechanical waves
B) Only electromagnetic waves
C) Only transverse waves
D) All types of waves

✅ Correct Answer: D

Explanation:
Superposition is a general property of waves, applying to mechanical, electromagnetic, transverse, and longitudinal waves.

Q4. When two waves of equal amplitude and frequency meet in phase, the result is:

A) Constructive interference
B) Destructive interference
C) Stationary waves
D) Beats

✅ Correct Answer: A

Explanation:
When waves meet in phase, crest meets crest, increasing amplitude — this is constructive interference.

Q5. Destructive interference occurs when two waves meet with a phase difference of:

A) 0°
B) 90°
C) 180°
D) 360°

✅ Correct Answer: C

Explanation:
A phase difference of 180° means crest meets trough, causing cancellation.

Q6. When two waves interfere destructively, the resultant amplitude is:

A) Greater than either wave
B) Less than either wave
C) Equal to the sum of the amplitudes
D) Zero, if perfectly out of phase and equal amplitude

✅ Correct Answer: D

Explanation:
For equal amplitudes and perfect opposite phase, the waves cancel completely, giving zero amplitude.

Q7. Constructive interference occurs when:

A) Two waves cancel each other
B) Two waves are in phase
C) Two waves have different amplitudes
D) Two waves are out of phase by 180°

✅ Correct Answer: B

Explanation:
Constructive interference occurs when waves are in phase, reinforcing each other.

Q8. The phenomenon which is not explained by the superposition principle:

A) Reflection of light
B) Interference of sound
C) Formation of beats
D) Stationary waves

✅ Correct Answer: A

Explanation:
Reflection is explained by laws of reflection, not superposition. Interference, beats, and stationary waves rely on superposition.

Q9. When two identical waves superpose in phase, the resultant is:

A) Destructive interference
B) Complete cancellation
C) A wave of reduced amplitude
D) Constructive interference

✅ Correct Answer: D

Explanation:
Identical waves in phase add up to produce maximum amplitude → constructive interference.

Q10. What type of interference occurs when crest meets trough of equal amplitude?

A) Constructive
B) Destructive
C) Stationary
D) Resonant

✅ Correct Answer: B

Explanation:
Crest meeting trough cancels displacement → destructive interference.

Q11. In superposition of waves, interference is said to be constructive when the waves:

A) Are of different types
B) Are exactly out of phase
C) Arrive at a point with crest meeting crest
D) Travel in opposite directions

✅ Correct Answer: C

Explanation:
Crest meeting crest increases amplitude, resulting in constructive interference.

Q12. The phenomenon of interference occurs in:

A) Sound waves only
B) Visible light waves only
C) All types of waves
D) Radio waves only

✅ Correct Answer: C

Explanation:
Interference is a wave property and occurs in all waves.

Q13. An antinode in a stationary wave is:

A) A point of maximum displacement
B) A point of minimum displacement
C) A point of zero displacement
D) A point of infinite displacement

✅ Correct Answer: A

Explanation:
Antinodes are points where particles vibrate with maximum amplitude.

Q14. Harmonics are:

A) Integer multiples of a fundamental frequency
B) Integer submultiples of a fundamental frequency
C) Random frequencies
D) Non-integer multiples of a fundamental frequency

✅ Correct Answer: A

Explanation:
Harmonics are frequencies equal to whole number multiples of the fundamental frequency.

Q15. When two identical waves move in opposite directions they give rise to:

A) Stationary waves
B) Beats
C) Constructive interference
D) Destructive interference

✅ Correct Answer: A

Explanation:
Oppositely moving identical waves form stationary (standing) waves.

Q16. On increasing the tension, the frequency of vibration of a string:

A) Increases
B) Decreases
C) Remains constant
D) First increases then decreases

✅ Correct Answer: A

Explanation:
Frequency of a stretched string is proportional to the square root of tension $f \propto \sqrt{T}$ f∝T

So, increasing tension increases frequency.

Q17. In stationary waves, the velocity of particle at the node is:

A) Maximum
B) Infinite
C) Variable
D) Zero

✅ Correct Answer: D

Explanation:
At a node, particles do not vibrate, hence velocity is zero.

Q18. At the open end of an organ pipe:

A) Nodes are formed
B) Antinodes are formed
C) Antinodes may be formed
D) Neither is formed

✅ Correct Answer: B

Explanation:
At the open end, air is free to move → displacement antinode.

Q19. A stationary wave is established if a string vibrates in four segments at a frequency of 120 Hz. Its fundamental frequency is:

A) 15 Hz
B) 30 Hz
C) 60 Hz
D) 450 Hz

✅ Correct Answer: B

Explanation:
Four segments = 4th harmonic $f_4 = 4f_1 \Rightarrow f_1 = 120/4 = 30\,Hz$ f4=4f1⇒f1=120/4=30Hz

Q20. A set of frequencies which are multiples of fundamental frequency is called:

A) Beat frequency
B) Harmonics
C) Nodal frequency
D) Doppler frequency

✅ Correct Answer: B

Explanation:
Frequencies equal to integer multiples of the fundamental are called harmonics.

Q21. The point of maximum displacement on stationary wave is:

A) Antinode
B) Node
C) Trough
D) Crest

✅ Correct Answer: A

Explanation:
Maximum displacement occurs at antinodes.

Q22. The fixed ends of vibrating string are:

A) Antinodes
B) Nodes
C) Overtones
D) Neither node nor antinode

✅ Correct Answer: B

Explanation:
Fixed ends cannot vibrate → nodes.

Q23. For same mass per unit length, if tension is increased 4 times, frequency becomes:

A) 2 times
B) 4 times
C) 6 times
D) 8 times

✅ Correct Answer: A

Explanation: $f \propto \sqrt{T} \Rightarrow \sqrt{4} = 2$ f∝T⇒4=2

Q24. A stretched string of length 2 m vibrates in 2 segments. Distance between consecutive nodes is:

A) 1 m
B) 2 m
C) 0.5 m
D) 4 m

✅ Correct Answer: A

Explanation:
2 segments → 2 loops → 3 nodes
Distance = Length / segments = 2 / 2 = 1 m

Q25. Number of nodes between two consecutive antinodes is:

A) One
B) Two
C) Three
D) Four

✅ Correct Answer: A

Explanation:
Between two antinodes, there is always one node.

Q26. A stretched string 4 m long has 4 loops. Wavelength is:

A) 1 m
B) 2 m
C) 3 m
D) 4 m

✅ Correct Answer: B

Explanation:
One loop = λ/2 $4 = 4(\lambda/2) \Rightarrow \lambda = 2\,m$ 4=4(λ/2)⇒λ=2m

Q27. In a stretched string, if speed of wave is doubled, tension becomes:

A) 2 times
B) 4 times
C) 8 times
D) 6 times

✅ Correct Answer: B

Explanation: $v \propto \sqrt{T} \Rightarrow T \propto v^2$ v∝T⇒T∝v2

Doubling speed → tension ×4

Q28. If a stretched string is 4 m and has 4 loops, the wavelength is:

A) 1 m
B) 2 m
C) 3 m
D) 4 m

✅ Correct Answer: B

Explanation:
Same as Q26 → 2 m

Q29. Waves produced in organ pipes are:

A) Transverse stationary waves
B) Longitudinal stationary waves
C) Electromagnetic waves
D) Matter waves

✅ Correct Answer: B

Explanation:
Sound waves in air are longitudinal stationary waves.

Q30. Two identical waves moving in same direction produce:

A) Interference
B) Beats
C) Stationary waves
D) Diffraction

✅ Correct Answer: A

Explanation:
Same direction waves overlap → interference.

Q31. A transverse wave reflecting from a denser medium changes phase by:

A) 360°
B) 180°
C) 90°
D) 0°

✅ Correct Answer: B

Explanation:
Reflection from denser medium causes phase reversal (180°).

Q32. When string is plucked from one-quarter length, it vibrates in:

A) One loop
B) Two loops
C) Three loops
D) Four loops

✅ Correct Answer: C

Explanation:
Plucking at 1/4 length produces 3 loops.

Q33. In a pipe open at both ends, displacement node is at:

A) Centre
B) Both ends
C) One end only
D) No displacement node

✅ Correct Answer: A

Explanation:
Open ends → antinodes
Centre → node

Q34. In a pipe closed at one end, possible harmonics are:

A) Even only
B) Odd only
C) All
D) None

✅ Correct Answer: B

Explanation:
Closed pipe supports odd harmonics only.

Q35. In an open pipe, antinodes in third harmonic are:

A) 1
B) 2
C) 3
D) 4

✅ Correct Answer: C

Explanation:
Nth harmonic in open pipe has n antinodes.

Q36. Which pipe produces both even and odd harmonics?

A) Open at one end
B) Closed at one end
C) Open at both ends
D) None

✅ Correct Answer: C

Q37. Harmonic not possible in closed pipe is:

A) First
B) Second
C) Third
D) Fifth

✅ Correct Answer: B

Q38. Harmonics present in closed pipe are:

A) Even only
B) Odd only
C) All
D) None

✅ Correct Answer: B

Q39. Node is a point where:

A) Amplitude is maximum
B) Phase changes
C) Medium remains stationary
D) Speed is maximum

✅ Correct Answer: C

Q40. Second harmonic of string has:

A) One antinode
B) Two antinodes
C) Two antinodes & three nodes
D) Three antinodes & two nodes

✅ Correct Answer: B

Q41. Speed of sound in air column depends on:

A) Material of pipe
B) Colour
C) Temperature
D) Diameter

✅ Correct Answer: C

Q42. Bending of waves around obstacles is called:

A) Refraction
B) Reflection
C) Diffraction
D) Interference

✅ Correct Answer: C

Q43. Diffraction occurs in:

A) Sound only
B) Light only
C) Water only
D) All waves

✅ Correct Answer: D

Q44. Diffraction increases by:

A) Increasing frequency
B) Wider slit
C) Shorter wavelength
D) Longer wavelength

✅ Correct Answer: D

Q45. Diffraction causes wave to:

A) Accelerate
B) Refract
C) Spread out
D) Disappear

✅ Correct Answer: C

Q46. Diffraction of sound causes:

A) Sound heard behind object
B) Blocked sound
C) Louder sound
D) Higher frequency

✅ Correct Answer: A

Q47. Diffraction in ripple tank depends on:

A) Depth only
B) Gap width & wavelength
C) Light speed
D) Angle

✅ Correct Answer: B

Q48. Narrower gap makes diffraction:

A) Less
B) More
C) Same
D) Blocked

✅ Correct Answer: B

Q49. Ripple tank is used to study:

A) Light refraction
B) Solid waves
C) Sound waves
D) Water surface waves

✅ Correct Answer: D

Q50. Waves in ripple tank are:

A) Longitudinal
B) Transverse
C) EM
D) Seismic

✅ Correct Answer: B

Q51. When water waves pass from deep to shallow regions in a ripple tank, they:

A) Speed up and wavelength increases
B) Slow down and wavelength decreases
C) Change direction and frequency increases
D) Reflect completely

✅ Correct Answer: B

Explanation:
In shallow water, wave speed decreases. Since frequency remains constant, wavelength must decrease

$v = f\lambda$ v=fλ

$f =$ f=

$\lambda =$ λ=λ

Q52. In a ripple tank, the frequency of waves is increased by:

A) Increasing water depth
B) Using a small wave generator
C) Increasing power to vibrator
D) Narrowing the slit

✅ Correct Answer: C

Explanation:
Frequency depends on the vibrator, not water depth or slit width. Increasing power increases frequency.

Q53. The result of constructive interference between two waves is:

A) Decrease in amplitude
B) Increase in amplitude
C) No change in amplitude
D) Phase shift

✅ Correct Answer: B

Explanation:
In constructive interference, amplitudes add up, producing greater amplitude.

Q54. If the amplitude of a wave is tripled, the energy becomes:

A) 3 times
B) 6 times
C) 9 times
D) 12 times

✅ Correct Answer: C

Explanation:
Energy ∝ (Amplitude)² $(3A)^2 = 9A^2$ (3A)2=9A2

Q55. The typical frequency range of microwaves is:

A) 10⁸ – 10⁹ Hz
B) 10⁶ – 10⁸ Hz
C) 10⁹ – 10¹⁰ Hz
D) 10⁹ – 10¹¹ Hz

✅ Correct Answer: D

Explanation:
Microwaves lie between radio waves and infrared waves (≈10⁹–10¹¹ Hz).

Q56. Beats can be heard when difference of frequency is not more than:

A) 4 Hz
B) 10 Hz
C) 14 Hz
D) 6 Hz

✅ Correct Answer: A

Explanation:
Human ear can detect beats clearly only when frequency difference ≤ 4 Hz.

Q57. To produce beats, two sound waves should have:

A) Same amplitude
B) Slightly different amplitudes
C) Same frequencies
D) Slightly different frequencies

✅ Correct Answer: D

Explanation:
Beats occur due to interference of waves with slightly different frequencies.

Q58. Two tuning forks of 240 Hz and 243 Hz produce beats per second:

A) 0
B) 4
C) 3
D) 2

✅ Correct Answer: C

Explanation: $\text{Beat frequency} = |243 – 240| = 3\,Hz$ Beat frequency=∣243−240∣=3Hz

Q59. Two identical tuning forks operating together produce beats per second:

A) 0
B) 1
C) 2
D) 3

✅ Correct Answer: A

Explanation:
Identical frequencies → no beat formation.

Q60. Beats are used to find:

A) Frequency
B) Wavelength
C) Speed
D) Intensity

✅ Correct Answer: A

Explanation:
Beats help determine unknown frequency by comparison.

Q61. Periodic increase and decrease in loudness is called:

A) Resonance
B) Interference
C) Beats
D) Polarization

✅ Correct Answer: C

Explanation:
Beats cause loudness to rise and fall periodically.

Q62. Due to interference of sound waves of same frequency, which changes?

A) Frequency
B) Time period
C) Wavelength
D) Amplitude

✅ Correct Answer: D

Explanation:
Interference changes amplitude, not frequency or wavelength.

Q63. The basic principle of beats is:

A) Interference
B) Diffraction
C) Reflection
D) Refraction

✅ Correct Answer: A

Explanation:
Beats result from interference of two waves.

Q64. Loading tuning fork prongs with wax causes frequency to:

A) Increase
B) Decrease
C) Remain same
D) Increase then decrease

✅ Correct Answer: B

Explanation:
Adding mass increases inertia, lowering frequency.

Q65. Pitch of sound depends on:

A) Intensity
B) Wavelength
C) Frequency
D) Loudness

✅ Correct Answer: C

Explanation:
Higher frequency → higher pitch.

Wave Intensity

Q66. Beats per second equal to:

A) Sum of frequencies
B) Ratio of frequencies
C) Either frequency
D) Difference of frequencies

✅ Correct Answer: D

Q67. Frequencies 261 Hz and 258 Hz produce beats per second:

A) 3
B) 2
C) 261
D) 258

✅ Correct Answer: A

Q68. Human ear recognizes beats up to:

A) 40 Hz
B) 30 Hz
C) 5 Hz
D) 10 Hz

✅ Correct Answer: C

Q69. Beats are caused by:

A) Reflection
B) Diffraction
C) Doppler effect
D) Interference

✅ Correct Answer: D

Q70. Time between two beats is called:

A) Frequency
B) Wavelength
C) Beat period
D) Resonance

✅ Correct Answer: C

Q71. In beats, amplitude of resultant wave:

A) Constant
B) Varies with time
C) Continuously increases
D) Continuously decreases

✅ Correct Answer: B

Q72. Beat frequency equals:

A) Sum
B) Average
C) Product
D) Difference

✅ Correct Answer: D

Q73. Intensity in beats:

A) Constant
B) Varies periodically
C) Increases
D) Decreases

✅ Correct Answer: B

Q74. Beats are not audible when:

A) Frequencies differ greatly
B) Amplitudes equal
C) Frequencies close
D) Waves in phase

✅ Correct Answer: A

Q75. Intensity of a wave is:

A) Total energy
B) Power per unit area
C) Speed
D) Displacement

✅ Correct Answer: B

Q76. Intensity is proportional to:

A) Amplitude
B) Amplitude²
C) Frequency
D) Wavelength

✅ Correct Answer: B

Q77. If amplitude doubles, intensity becomes:

A) Half
B) Double
C) Four times
D) Same

✅ Correct Answer: C

Q78. SI unit of intensity:

A) Watt
B) Newton
C) W/m²
D) Joule

✅ Correct Answer: C

Q79. Which does NOT affect intensity?

A) Distance
B) Frequency
C) Amplitude
D) Medium absorption

✅ Correct Answer: B

Q80. Doubling distance from source causes intensity to:

A) Double
B) Half
C) One-fourth
D) Same

✅ Correct Answer: C

Q81. Intensity measures:

A) Loudness only
B) Wavelength
C) Phase difference
D) Energy per second per area

✅ Correct Answer: D

Q82. Intensity decreases as:

A) Frequency increases
B) Source approaches
C) Distance increases
D) Wavelength increases

✅ Correct Answer: C

Doppler Effect

Q83. Doppler Effect in astronomy is used to:

A) Measure star diameter
B) Determine velocity of galaxies
C) Study black holes
D) Study EM behavior

✅ Correct Answer: B

Q84. Doppler effect applies to:

A) Sound only
B) Light only
C) Sound & EM waves
D) Water waves

✅ Correct Answer: C

Q85. Source moving towards observer causes:

A) Lower frequency
B) Same frequency
C) Higher frequency
D) No sound

✅ Correct Answer: C

Q86. Doppler effect is used in:

A) Blood flow
B) Radar
C) Astronomy
D) All

✅ Correct Answer: D

Q87. Source moving away causes wavelength to:

A) Increase
B) Decrease
C) Constant
D) Zero

✅ Correct Answer: A

Q88. Doppler effect is change in:

A) Wavelength due to interference
B) Frequency due to motion
C) Speed
D) Amplitude

✅ Correct Answer: B

Q89. Observer moving away hears:

A) Higher frequency
B) Lower frequency
C) Same
D) Zero

✅ Correct Answer: B

Q90. Waves used in SONAR are:

A) UV
B) Ultrasonic
C) Radio
D) Microwave

✅ Correct Answer: B

Q91. RADAR is application of:

A) Chemical effect
B) Electric effect
C) Doppler effect
D) Magnetic effect

✅ Correct Answer: C

Q92. Star moving toward Earth shows:

A) Blue shift
B) Red shift
C) No shift
D) Longer wavelength

✅ Correct Answer: A

Q93. Siren frequency increases for listener if:

✅ Correct Answer: B

Explanation:
Listener is behind but moving faster → source appears approaching.

Q94. Submarine location is detected by:

A) Doppler effect
B) Temperature
C) Diffraction
D) Compton

✅ Correct Answer: A

Q95. Star moving away shows:

A) Green shift
B) Blue shift
C) Red shift
D) Yellow shift

✅ Correct Answer: C

Q96. Waves used in SONAR are:

A) Sound waves
B) Light
C) Heat
D) Water

✅ Correct Answer: A

Q97. RADAR system uses:

A) Electric
B) Doppler
C) Magnetic
D) Chemical

✅ Correct Answer: B

Q98. Waves used in SONAR are:

A) Sound
B) Light
C) Heat
D) Water

✅ Correct Answer: A

Q99. Apparent frequency heard is:

A) 60 Hz
B) 200 Hz
C) 100 Hz
D) 150 Hz

✅ Correct Answer: D

Q100. Red shift indicates universe is:

A) Expanding
B) Contracting
C) Stationary
D) Oscillating

✅ Correct Answer: A

Q101. Equation with same dimensions is:

A) Simultaneous
B) Homogeneous
C) Instantaneous
D) Quadratic

✅ Correct Answer: B

Q102. Star wavelength longer than lab value means star is:

A) Moving away
B) Moving toward
C) Stationary
D) Revolving

✅ Correct Answer: A

Q103. Speed of wave is:

A) 125 m/s
B) 250 m/s
C) 500 m/s
D) 1000 m/s

✅ Correct Answer: C

Q104. Ambulance moving in circle heard by center observer:

A) Same frequency
B) Lower
C) Higher
D) Changing

✅ Correct Answer: A