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Wave Phenomena Revision for IB Physics

May 27, 2025

SL IB Physics - Wave Phenomena Revision Notes

Contents

  • Wavefronts & Rays
  • Reflection, Refraction & Transmission
  • Diffraction of Waves
  • Refraction of Waves
  • Superposition of Waves
  • Interference of Waves
  • Young's Double-Slit Experiment

Wavefronts & Rays

  • Waves travel in two or three dimensions:
    • Surface waves (2D) have circular wavefronts.
    • Spherical waves (3D) have spherical wavefronts.
  • Graphical Representation:
    • Wavefronts: Lines joining in-phase points, perpendicular to motion.
    • Rays: Lines showing wave motion, perpendicular to wavefront.
  • Transverse Waves: Show parallel vertical lines for wavefronts viewed from above.
    • Peaks and troughs represented by darker and fainter lines, respectively.
  • Exam Tip: Draw wavefronts/rays with a ruler to ensure clarity.

Reflection, Refraction & Transmission

  • At Boundaries: Waves can be reflected, refracted, transmitted, or absorbed.
  • Reflection:
    • Occurs when a wave hits a boundary and bounces back.
    • Law of Reflection: Angle of incidence (i = ) Angle of reflection (r).
    • Frequency, wavelength, and speed remain unchanged during reflection.
  • Refraction:
    • Change in wave direction when passing through media with different densities.
    • Affected by speed changes of wavefront parts at the boundary.
    • Light bends towards/away from the normal when moving between different densities.
  • Transmission: General term for wave passing through a substance.
    • Involves partial absorption and unchanged wave frequency.
  • Exam Tip: Differentiate between refraction and reflection; refraction involves a medium change.

Diffraction of Waves

  • Definition: Spreading of waves as they pass through a gap or around barriers.
  • Through an Aperture:
    • Greater diffraction when wavelength is similar to gap width.
    • Little to no diffraction if the gap size and wavelength are not similar.
  • Around a Barrier:
    • Extent depends on wavelength; longer wavelengths undergo more diffraction.
    • "Shadow" regions form behind barriers with less diffraction.
  • Worked Example: Demonstrates diffraction based on wavelength proximity to aperture size.

Refraction of Waves

  • Snell's Law: Relates angles of incidence and refraction at media boundaries.
  • Refractive Index (n):
    • Indicates optical density; higher (n) means slower light travel.
    • Calculated as (n = \frac{c}{v}), where (c) is speed of light in vacuum, (v) in medium.
  • Critical Angle & Total Internal Reflection:
    • Critical angle (c) is where light is refracted along the boundary.
    • Total internal reflection occurs when incidence angle > critical angle.
  • Exam Tip: Ensure calculator is in degrees mode for angle calculations.

Superposition of Waves

  • Principle: Combined amplitude at a point equals the sum of individual wave displacements.
  • Interference:
    • Result of superposition; can be constructive (adding) or destructive (cancelling).
  • Worked Example: Illustration of superposition with overlapping waves.

Interference of Waves

  • Double Source Interference:
    • Uses coherent sources or a single source with a double slit to create interference patterns.
    • Seen in laser beams, speakers, microwaves.
  • Interference Types:
    • Constructive: Waves meet peak-to-peak.
    • Destructive: Waves meet peak-to-trough.
  • Coherence: Requires same frequency and constant phase difference.

Young's Double-Slit Experiment

  • Setup:
    • Involves coherent light through a double slit creating a diffraction pattern.
    • Results in bright (constructive) and dark (destructive) fringes on a screen.
  • Interference Pattern:
    • Defined by path differences and calculated using the double-slit equation.

General Tips

  • Path Difference: Refers to the difference in distance traveled by waves from different sources.
  • Equation Use: Be familiar with wave equations and their applications in practical problems.
  • Examiner Tips: Always ensure clarity in diagrams and verify calculations for logical inconsistencies.