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PHYSICS, M3 2023 VCE 16 MC

Water waves travelling at constant speed and hitting a barrier can change direction, as shown in the diagram below.
 

Which one of the following best identifies this phenomenon?

  1. diffraction
  2. dispersion
  3. refraction
  4. resonance
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\(A\)

Show Worked Solution
  • Diffraction is the phenomena that can describe when waves bend around a corner after they pass a barrier, as can be observed in the diagram.

\(\Rightarrow A\)

PHYSICS, M3 2017 VCE 14 MC

A teacher stands in the corridor at a short distance from the open door of her classroom, as shown in the diagram below. She can hear her students. but cannot see them.
 

Which one of the following best explains why the teacher can hear her students?

  1. The speed of sound is much greater than the speed of light.
  2. The speed of sound is comparable with the speed of light.
  3. Sound diffracts because the wavelength of sound is much smaller than the width of the door.
  4. Sound diffracts because the wavelength of sound is comparable with the width of the door.
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\(D\)

Show Worked Solution
  • Sound waves can range anywhere from 20mm to 17m and thus the some sounds made by the students would have a wavelength of 1 metre.
  • Therefore, sound will diffract through the doorway as it is the same order of magnitude of the size of the door whereas light will not as its wavelengths are much smaller in size.

\(\Rightarrow D\)

PHYSICS, M3 2020 VCE 14 MC

Students are investigating the diffraction of waves using a ripple tank. Water waves are directed towards barriers with gaps of different sizes, as shown below.

In which one of the following would the greatest diffraction effects be observed?
 

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\(B\)

Show Worked Solution
  • The greatest diffraction patterns are observed when the wavelength is the same size as the slit through which the wave passes.

\( \Rightarrow B\)

PHYSICS, M3 2022 VCE 16

A small sodium lamp, emitting light of wavelength 589 nm, is viewed at night through two windows from across a street. The glass of one window has a fine steel mesh covering it and the other window is open, as shown in Figure 18. Assume that the sodium lamp is a point source at a distance.

A Physics student is surprised to see a pattern formed by the light passing through the steel mesh but no pattern for the light passing through the open window. She takes a photograph of the observed pattern to show her teacher, who assures her that it is a diffraction pattern.
 

  1. State the condition that the fine steel mesh must satisfy for a diffraction pattern to form.  (1 mark)
  1. Explain why the condition stated in part a. does not apply to the open window.  (2 marks)
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a.   Condition to satisfy:

  • The size of the gaps from the fine steel mesh must be of the same order of magnitude of the wavelengths of the light from the sodium lamp.

b.   Open window differences:

  • The width of the window is significantly greater than wavelength of the light from the sodium lamp and the width of the glass molecules that make up the glass window is significantly smaller than the light from the sodium lamp.
  • These widths contrast greatly to the size of the steel mesh and are not of the same order of magnitude of the light from the sodium lamp, hence no diffraction will occur.
Show Worked Solution

a.   Condition to satisfy:

  • The size of the gaps from the fine steel mesh must be of the same order of magnitude of the wavelengths of the light from the sodium lamp.

b.   Open window differences:

  • The width of the window is significantly greater than wavelength of the light from the sodium lamp and the width of the glass molecules that make up the glass window is significantly smaller than the light from the sodium lamp.
  • These widths contrast greatly to the size of the steel mesh and are not of the same order of magnitude of the light from the sodium lamp, hence no diffraction will occur.
♦ Mean mark (b) 40%.