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.