AQA Waves for A-Level Physics Lecture Notes

Key Concepts

• Oscillations in Media
  • Amplitude: Maximum displacement from equilibrium.
  • Frequency: Number of completed cycles per unit time. SI unit is Hertz (Hz).
  • Wavelength: Distance between two points in phase on a wave.
  • Wave Speed: Distance traveled by the wave per unit time. Calculated using wave speed = frequency × wavelength.
  • Phase: Fraction of a cycle covered, measured in degrees or radians.
  • Phase Difference: Difference between the phases of two points.

Concepts of Waves

• Transverse Waves: Oscillations perpendicular to energy transfer direction.
• Longitudinal Waves: Oscillations parallel to energy transfer direction.
• Polarization: Oscillations restricted to a single plane; only transverse waves can be polarized.
  • Applications: Polaroids, reducing glare, communication systems.

Wave Interactions

• Superposition: The resultant displacement is the vector sum of individual displacements.
• Interference: Superposition of waves leading to maxima (constructive) and minima (destructive).
• Coherence: Constant phase difference and same frequency.

Young's Double Slit Experiment

• Setup: Use of coherent sources or single source with double slits.
• Interference Pattern: Alternating fringes of maxima and minima.
• Young's Equation: W = λD/s, where:
  • W = Fringe separation
  • λ = Wavelength
  • D = Distance from slits to screen
  • s = Slit spacing

Diffraction and Gratings

• Diffraction: Spreading of light passing through a gap.
• Single Slit Diffraction: Wide central maximum with narrower side fringes.
• Diffraction Grating: Multiple slits producing distinct patterns.
  • Equation: d sin θ = nλ, where d = slit spacing.
  • Applications: Analyzing atomic spectra, x-ray crystallography.

Refraction and Total Internal Reflection

• Refractive Index: Ratio of speed of light in vacuum to speed in a substance.
• Snell's Law: n₁sinθ₁ = n₂sinθ₂.
• Critical Angle: Angle of incidence above which total internal reflection occurs.
• Fiber Optics: Use total internal reflection to transmit light efficiently.
  • Core and Cladding: Low absorption, prevent dispersion.

Harmonics and Stationary Waves

• Formation: Incident wave reflects and superposes with itself.
• Harmonics: Frequencies that are multiples of the fundamental frequency.
• Stationary vs. Progressive Waves: Energy stored vs. energy transfer.

Example Problems and Insights

• Understanding phase differences and path differences in interference patterns.
• Calculating maximum orders in diffraction gratings.
• Analyzing polarization effects and wave interference in real-world applications.

Summary

• Review of wave concepts is crucial, especially for exams.
• Understand practical applications and calculations for wave behavior and interactions.

These notes should provide a comprehensive overview of the wave-related topics covered in the lecture, serving as a useful study guide.