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STD 11 - 14. waves and sound — JEE STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceJEESTD 11 - 14. waves and sound4 Marks
MCQ
As a wave propagates
  • A
    The wave intensity remains constant for a plane wave
  • B
    The wave intensity decreases as the inverse of the distance from the source for a spherical wave
  • ✓
    The wave intensity decreases as the inverse of square of the distance from the source for a spherical wave
  • D
    Total intensity of the spherical wave over the spherical surface centred at the source remains constant at all time
✓

Answer

Correct option: C.
The wave intensity decreases as the inverse of square of the distance from the source for a spherical wave
c
A plane wave does not have any radial dependence. Thus a plane wave travels with constant intensity. Intensity of a spherical wave decreases. It is because the power in the wave is carried and constant at all radius. Intensity is power distributed over the spherical surface area.

$I=\frac{P}{4 \pi r^{2}}$

For a cylindrical wave the power is same at all distance from the source. The power is distributed over the entire surface area.

$I=\frac{P}{2 \pi r l}$

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