B Tech Applied Science - Unit 1 Physics: Wave Interference

Introduction to Wave Interference

• Concept: Understanding wave interference using sound waves from speakers.
• Setup:
  • Single speaker emitting a sound, perceived as a single note by the observer.
  • Two speakers (coherent sources) emitting the same frequency, amplitude, and in phase.

Coherent Sources

• Coherent Sources: Two sources doing exactly the same thing at the same time.
• Impact:
  • The observer might expect louder sound with two speakers.
  • Reality: In some places sound is louder, in others, it's quieter.

Principle of Superposition

• Key Concept: When waves from two sources meet, they add together.
• Constructive Interference:
  • Occurs when waves arrive in phase (up and down together).
  • Results in a larger wave and louder sound.
• Destructive Interference:
  • Occurs when waves arrive in antiphase (opposite movements).
  • Results in waves canceling each other out, leading to a quieter sound.

Examples of Wave Interference

• Visual Example:
  • Two diagrams showing waves from Source 1 and Source 2.
  • Constructive Interference: Waves in phase creating a big wave.
  • Destructive Interference: Waves in antiphase canceling each other.

Water Waves Example

• Scenario: Dripping tap as a point source producing circular water waves.
• Coherent Sources: Two point sources with same amplitude, frequency, and phase.
• Outcomes:
  • Constructive Interference: Occurs at some points (e.g., point x and zed).
  • Destructive Interference: Occurs at other points (e.g., point y).

Path Difference

• Definition: The difference in how far the waves have traveled.
• Constructive Interference:
  • Occurs when waves have traveled the same path or differ by a whole wavelength.
  • Example: Point x has waves traveling the same distance.
  • Point zed: Path difference equals one wavelength (e.g., 7 vs. 8 wavelengths).
• Destructive Interference:
  • Occurs when path difference is half a wavelength.
  • Example: Point y and along the green line.

Summary

• Understanding wave interference helps explain variations in sound intensity.
• Key factors include coherence, phase alignment, and path difference.