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Wave Optics — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsWave Optics4 Marks
Question
Wavefront is a locus of points which vibratic in same phase. A ray of light is perpendicular to the wavefront. According to Huygens principle, each point of the wavefront is the source of a secondary disturbance and the wavelets connecting from these points spread out in all directions with the speed of wave.
The figure shows a surface XY separating two transparent media, medium-I and medium-2. The lines ab and cd represent wavefronts of a light wave travelling in medium- 1 and incident on XY. The lines ef and gh represent wavefronts of the light wave in medium-2 after refraction.
  1. Light travels as a:
  1. Parallel beam in each medium.
  2. Convergent beam in each medium.
  3. Divergent beam in each medium.
  4. Divergent beam in one medium and convergent beam in the other medium.
  1. The phases of the light wave at c, d, e and f are $\phi_\text{c},\phi_\text{d},\phi_\text{e}$ and $\phi_\text{f}$ respectively. It is given that $\phi_\text{c}\not=\phi_\text{f}$
  1. $\phi_\text{c}$ cannot be equal $\phi_\text{d}$
  2. $\phi_\text{d}$ cannot be equal $\phi_\text{e}$
  3. $(\phi_\text{d}-\phi_\text{f})$ is equal to $(\phi_\text{c}-\phi_\text{e})$
  4. $(\phi_\text{d}-\phi_\text{c})$ is not equal to $(\phi_\text{f}-\phi_\text{e})$
  1. Wavefront is the locus of all points, where the particles of the medium vibrate with the same.
  1. Phase
  2. Amplitude
  3. Frequency
  4. Period
  1. A point source that emits waves uniformly in all directions, produces wavefronts that are:
  1. Spherical
  2. Elliptical
  3. Cylindrical
  4. Planar
  1. What are the types of wavefronts?
  1. Spherical
  2. Cylindrical
  3. Plane
  4. All of these.
✓

Answer

  1. (a) Parallel beam in each medium.
Explanation:
Since the path difference between two waveform is equal, light traves as parallel beam in each medium.
  1. (c) $(\phi_\text{d}-\phi_\text{f})$ is equal to $(\phi_\text{c}-\phi_\text{e})$
Explanation:
Since all points on the wavefront are in the same phase,
$\phi_\text{d}=\phi_\text{c}$ and $\phi_\text{f}=\phi_\text{e}$
$\therefore\phi_\text{d}-\phi_\text{f}=\phi_\text{c}-\phi_\text{e}$
  1. (a) Phase
Explanation:
Wavefront is the locus of all points, where the particles of the medium vibrate with the same phase.
  1. (a) Spherical
  1. (d) All of these.

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