MCQs / Physics / Wave Intensity and the Doppler Effect

Wave Intensity and the Doppler Effect MCQs — Physics (page 3)

60 multiple-choice questions on Wave Intensity and the Doppler Effect 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. A progressive wave has intensity 4 W/m^2. If its amplitude is multiplied by 2, its new intensity is:

  1. 32 W/m^2
  2. 8 W/m^2
  3. 16 W/m^2
  4. 160 W/m^2

Answer: C) 16 W/m^2

Explanation: I propto A^2, so I = 4 (2)^2 = 16 W/m^2. SLO P-11-D-01 · Application

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52. A stationary source of sound produces:

  1. no Doppler shift for a stationary observer
  2. a lower pitch
  3. beats
  4. a higher pitch

Answer: A) no Doppler shift for a stationary observer

Explanation: No relative motion. SLO P-11-D-02 · Understanding

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53. A point source radiates 1 W of sound equally in all directions. The intensity 10 m away is:

  1. 7.96 10^-4 W/m^2
  2. 0.00318 W/m^2
  3. 0.0025 W/m^2
  4. 0.00796 W/m^2

Answer: A) 7.96 10^-4 W/m^2

Explanation: I = P4pi r^2 = 14pi(10)^2 = 7.96 10^-4 W/m^2. SLO P-11-D-01 · Application

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54. If you double your distance from a point source, the intensity becomes:

  1. double
  2. half
  3. one quarter
  4. unchanged

Answer: C) one quarter

Explanation: Inverse square law. SLO P-11-D-01 · Application

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55. Behind a moving source, the observed wavelength is:

  1. zero
  2. shorter
  3. the same
  4. longer

Answer: D) longer

Explanation: Waves are spread out. SLO P-11-D-02 · Understanding

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56. The rotation of a star or a galaxy can be detected because:

  1. it stops emitting
  2. one side shows a red shift and the other a blue shift
  3. it changes colour completely
  4. it becomes brighter

Answer: B) one side shows a red shift and the other a blue shift

Explanation: One side approaches, the other recedes. SLO P-11-D-04 · Understanding

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57. If the source moves faster towards a stationary listener, the observed frequency:

  1. is unchanged
  2. increases further
  3. becomes zero
  4. decreases

Answer: B) increases further

Explanation: Wavefronts are squashed more. SLO P-11-D-02 · Understanding

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58. Doppler ultrasound is used in hospitals to:

  1. measure blood sugar
  2. take X-ray images
  3. measure the speed of blood flow and study heart problems
  4. measure body temperature

Answer: C) measure the speed of blood flow and study heart problems

Explanation: Reflections from moving blood cells are shifted. SLO P-11-D-04 · Understanding

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59. In fo = fs vv pm vs, the minus sign is used when the source:

  1. is stationary
  2. moves towards the observer
  3. moves perpendicular
  4. moves away from the observer

Answer: B) moves towards the observer

Explanation: Smaller denominator gives a higher frequency. SLO P-11-D-03 · Application

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60. Astronomers use the Doppler effect to:

  1. find how fast stars and galaxies move towards or away from us
  2. count stars
  3. find the colour of stars
  4. measure the mass of planets directly

Answer: A) find how fast stars and galaxies move towards or away from us

Explanation: Red shift and blue shift. SLO P-11-D-04 · Understanding

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