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Superposition, Stationary Waves and Beats MCQs — Physics (page 3)

150 multiple-choice questions on Superposition, Stationary Waves and Beats from Physics, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

51. In a ripple tank, water waves pass through a gap much wider than their wavelength. They:

  1. reflect back
  2. spread out a lot
  3. spread very little
  4. stop completely

Answer: C) spread very little

Explanation: Mostly straight through. SLO P-11-D-13 · Understanding

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52. Two waves of amplitudes 4 cm and 4 cm meet with a phase difference of pi. The resultant amplitude is:

  1. 4 cm
  2. 8 cm
  3. 16 cm
  4. 0 cm

Answer: D) 0 cm

Explanation: Antiphase: complete cancellation. SLO P-11-D-08 · Understanding

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53. In a microwave stationary-wave experiment, adjacent nodes are 1.5 cm apart. The wavelength of the microwaves is:

  1. 3 cm
  2. 6 cm
  3. 1.5 cm
  4. 12 cm

Answer: A) 3 cm

Explanation: Node to node = lambda2, so lambda = 2 1.5 = 3 cm. SLO P-11-D-10 · Application

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54. Coherence is required for observing:

  1. refraction
  2. the Doppler effect
  3. a stable interference pattern
  4. reflection

Answer: C) a stable interference pattern

Explanation: Fixed pattern of maxima and minima. SLO P-11-D-14 · Understanding

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55. Beats are:

  1. regular rises and falls in loudness when two waves of slightly different frequency interfere
  2. the sound of a drum only
  3. echoes of a sound
  4. a change in pitch due to motion

Answer: A) regular rises and falls in loudness when two waves of slightly different frequency interfere

Explanation: Pulsation due to interference. SLO P-11-D-15 · Understanding

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56. The harmonics of a string fixed at both ends have frequencies in the ratio:

  1. 1 : 3 : 5 : 7 …
  2. 1 : 4 : 9 …
  3. 1 : 1 : 1 …
  4. 1 : 2 : 3 : 4 …

Answer: D) 1 : 2 : 3 : 4 …

Explanation: fn = nf1. SLO P-11-D-12 · Understanding

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57. Colours seen in a soap film are produced by:

  1. dispersion in a prism
  2. interference of light reflected from the two surfaces
  3. the Doppler effect
  4. polarization

Answer: B) interference of light reflected from the two surfaces

Explanation: Thin-film interference. SLO P-11-D-08 · Understanding

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58. Long-wave radio signals can be received behind hills because:

  1. long wavelengths diffract around the hills
  2. they are reflected by the ground
  3. they travel faster
  4. they are polarized

Answer: A) long wavelengths diffract around the hills

Explanation: Large wavelengths diffract a lot. SLO P-11-D-13 · Understanding

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59. Two tuning forks of 256 Hz and 260 Hz are sounded together. The number of beats heard per second is:

  1. 258
  2. 4
  3. 8
  4. 516

Answer: B) 4

Explanation: Beat frequency = f1 - f2 = 4 Hz. SLO P-11-D-15 · Understanding

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60. In Young's experiment, coherent sources are obtained by:

  1. dividing light from one source using two slits
  2. using sunlight directly with no slit
  3. using two separate lamps
  4. using two lasers of different colours

Answer: A) dividing light from one source using two slits

Explanation: Both slits get light from the same wavefront. SLO P-11-D-14 · Understanding

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61. Diffraction is:

  1. the bending of waves when they change speed
  2. the change of frequency of waves
  3. the spreading of waves as they pass through a gap or around an obstacle
  4. the bouncing back of waves

Answer: C) the spreading of waves as they pass through a gap or around an obstacle

Explanation: Not to be confused with refraction. SLO P-11-D-13 · Understanding

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62. Beats are heard only if the two frequencies differ by:

  1. a very large amount
  2. zero
  3. a small amount (less than about 10–15 Hz)
  4. exactly double

Answer: C) a small amount (less than about 10–15 Hz)

Explanation: Otherwise the ear hears two separate notes. SLO P-11-D-15 · Understanding

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63. An antinode in a stationary wave is a point of:

  1. zero frequency
  2. maximum amplitude
  3. zero energy
  4. zero amplitude

Answer: B) maximum amplitude

Explanation: Waves always reinforce there. SLO P-11-D-11 · Understanding

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64. At a point, one wave alone gives a displacement of 3 cm and another alone gives 2 cm. When both arrive, the displacement is:

  1. 3.61 cm
  2. 5 cm
  3. 1 cm
  4. 6 cm

Answer: B) 5 cm

Explanation: By superposition, displacements add: 3 + (2) = 5 cm. SLO P-11-D-07 · Application

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65. Beats are useful for tuning because:

  1. they change the speed of sound
  2. the human ear can detect very small frequency differences as slow beats
  3. they make sound louder permanently
  4. they polarize the sound

Answer: B) the human ear can detect very small frequency differences as slow beats

Explanation: Very sensitive method. SLO P-11-D-16 · Application

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66. The 'anti-noise' wave must have:

  1. twice the frequency of the noise
  2. the same frequency and amplitude as the noise but be 180^circ out of phase
  3. the same phase as the noise
  4. a much larger amplitude

Answer: B) the same frequency and amplitude as the noise but be 180^circ out of phase

Explanation: So the waves cancel. SLO P-11-D-09 · Understanding

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67. At a point, one wave alone gives a displacement of 4 cm and another alone gives -4 cm. When both arrive, the displacement is:

  1. 8 cm
  2. -16 cm
  3. 0 cm
  4. 5.66 cm

Answer: C) 0 cm

Explanation: By superposition, displacements add: 4 + (-4) = 0 cm. SLO P-11-D-07 · Application

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68. In a stationary wave of wavelength 60 cm, the distance between adjacent antinodes is:

  1. 120 cm
  2. 60 cm
  3. 15 cm
  4. 30 cm

Answer: D) 30 cm

Explanation: lambda2. SLO P-11-D-11 · Understanding

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69. Increasing the wavelength of waves passing through a fixed gap causes:

  1. the waves to stop
  2. more diffraction
  3. less diffraction
  4. no change

Answer: B) more diffraction

Explanation: Ratio lambda/gap increases. SLO P-11-D-13 · Understanding

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70. Two waves with frequencies 500 Hz and 502 Hz are:

  1. polarized
  2. identical
  3. coherent
  4. not coherent (their phase difference keeps changing)

Answer: D) not coherent (their phase difference keeps changing)

Explanation: They produce beats instead. SLO P-11-D-14 · Understanding

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71. The distance between two adjacent nodes is:

  1. 2lambda
  2. lambda4
  3. lambda
  4. lambda2

Answer: D) lambda2

Explanation: Same for adjacent antinodes. SLO P-11-D-11 · Understanding

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72. A pipe open at both ends has length 0.5 m (v = 340 m/s). Its fundamental frequency is:

  1. 340 Hz
  2. 85 Hz
  3. 170 Hz
  4. 680 Hz

Answer: A) 340 Hz

Explanation: f1 = v2L = 3401 = 340 Hz. SLO P-11-D-12 · Understanding

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73. Two coherent sources in phase emit waves of wavelength lambda. At a point, the path difference is 3.5lambda. The interference there is:

  1. constructive only for sound
  2. constructive
  3. destructive
  4. neither — there is no interference

Answer: C) destructive

Explanation: Path difference = nlambda gives constructive; (n + 12)lambda gives destructive. Here 3.5lambda ⇒ destructive. SLO P-11-D-07 · Application

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74. Two tuning forks of 512 Hz and 506 Hz are sounded together. The number of beats heard per second is:

  1. 1020
  2. 509
  3. 6
  4. 12

Answer: C) 6

Explanation: Beat frequency = f1 - f2 = 6 Hz. SLO P-11-D-15 · Understanding

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75. In a ripple tank, making the gap narrower (closer to the wavelength):

  1. changes their frequency
  2. stops the waves
  3. decreases the spreading
  4. increases the spreading

Answer: D) increases the spreading

Explanation: More diffraction. SLO P-11-D-13 · Understanding

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