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Waves & Optics · Physics

Interference patterns come from phase differences.

Use path difference to compute phase difference, then predict where constructive and destructive interference occur for two sources.

This topic

Interference of Waves

Learn the conditions for maxima and minima, then interpret beats as interference in time (intro).

Core
Path difference and phase difference
Interference is controlled by phase at a point. Path difference converts geometry into phase difference using the wavelength.
  • Path difference as a geometric quantity
  • Phase difference as “how out of step”
  • Wavelength sets the scale
  • Common unit and sign pitfalls
Start nano-lesson Convert geometry → phase using λ.
Conditions
Interference conditions
Maxima and minima occur at specific phase differences. Learn how to write the conditions clearly and interpret them physically.
  • Constructive condition (maxima)
  • Destructive condition (minima)
  • What “integer multiple” means
  • Why conditions are about phase, not amplitude
Start nano-lesson Write conditions first; solve second.
Two sources
Two-source interference
Two coherent sources produce stable patterns. Learn how to reason about which points are reinforced or canceled without getting lost in algebra.
  • Coherence requirement (conceptual)
  • Geometry-to-condition workflow
  • Locating maxima/minima qualitatively
  • Interpreting pattern spacing ideas
Start nano-lesson Coherence makes the pattern stable.
Time
Beats (intro)
Beats occur when two close frequencies overlap. The result is a rapidly oscillating signal with a slowly varying envelope.
  • Two nearby frequencies idea
  • Fast oscillation + slow envelope
  • Beat frequency interpretation
  • Where you see beats in practice
Start nano-lesson Beats are interference in time.
Practice
Practice & Exercises
Practice using path difference, applying interference conditions, and interpreting beats from graphs and descriptions.
  • Path-to-phase conversion drills
  • Maxima/minima condition applications
  • Two-source reasoning questions
  • Beats interpretation from time plots
  • Exam-style interference sets
Open practice Start with a labeled sketch.