Conditions for wave interference: reflection due to phase change

Physics > Conditions for wave disturbances: reflection due to phase change

Explore what is wave interference: conditions and results. Read about waves and noise, amplitude change, phase difference, wave patterns, formulas, reflection.

Interference (noise) is a phenomenon where two waves combine to increase or decrease the amplitude.

Learning challenge

  • Explain the difference between constructive and destructive interference.

Key points

  • If several waves hit a single point, then its total displacement is equated to the vector summation of individual ones.
  • If light passes from a vacuum to another medium, then it changes the speed and wavelength, but the frequency remains stable.
  • If the light bounces off a medium with a higher refractive index, the valleys will be reflected as ridges.


  • Serial – waves with a uniform direction, length and phase (like a laser).
  • Plane wave – wave fronts appear as infinite parallel planes with a stable amplitude, located perpendicular to the phase velocity vector.

Conditions for wave interference

Let’s take a close look at what interference is, as well as the conditions, properties and result of the phenomenon. With interference, two waves are superimposed to increase or decrease the amplitude. The effect can be seen in any type of wave. Typically, interference concerns the contact of waves that are in coherence, because they arise from a single source and have a similar frequency.

If two waves are at a single point, then its total displacement is equal to the summation of the individual displacements. If they converge on crests and frequencies, then the amount of displacement is the sum of the individual values. This is a constructive type of interference, where the phase difference = 2π. In a destructive form, the crest is superimposed on the depression, and then the magnitude of the displacements is the difference between individual values ​​(π).

Examples of constructive (left) and destructive (right) interference

A simple form of interference occurs when two waves of the same frequency intersect at an angle. They are located in the phase of point B, and the relative changes along the x axis. The phase difference is calculated as:

Geometric position of two plane wave interference

Structural disturbances occur when waves are in phase or

Destructive interference occurs when the waves are in half-cycle or

Reflection due to phase change

Light has wave properties and manifests them in different environments. When passing from a vacuum to another medium, the speed and wavelength change, but the frequency remains stable. The speed is calculated by the formula: v = c / n (n is the refractive index). For example, water has n = 1.333. If light is bounced off a higher refractive index, then the valleys are reflected as ridges.

Physics Section

Superposition and interference
  • Conditions for Wave Noise: Reflection due to Change in Variation
  • Air wedge
  • Newton’s rings
  • Huygens principle
  • Young’s double slit experiment
  • Diffraction gratings: X-ray, grating, reflection
  • Single slit diffraction
  • Rayleigh criterion
Further topics
  • Thin film interference
  • Light transmission through polarizers
  • Polarization by scattering and reflection
  • Light scattering by the atmosphere
  • Dispersion of the visible spectrum
Wave optics applications
  • Improving microscopy
  • Spectrometer
  • Michelson interferometer
  • LCD displays
  • Using interference with CDs and DVDs

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