Interference with Coherent and Incoherent Waves

Coherent waves:

• Have a constant phase difference.
• They are produced by a single source or by multiple sources that are in phase.
• They can interfere with each other to produce bright and dark fringes.

Incoherent waves:

• Have a random phase difference.
• They are produced by multiple sources that are not in phase.
• They cannot interfere with each other to produce bright and dark fringes.

Interference:

• Is the superposition of two or more waves.
• Can be constructive or destructive.

Constructive interference:

• Occurs when the waves are in phase.
• The resulting wave has a greater amplitude than the individual waves.

Destructive interference:

• Occurs when the waves are out of phase.
• The resulting wave has a smaller amplitude than the individual waves.

Path difference:

• Is the difference in the distances that two waves travel from their sources to a point of observation.

Phase difference:

• Is the difference in the phases of two waves at a point of observation.

Young’s double-slit experiment:

• Is a classic experiment that demonstrates the interference of light waves.
• Produces a fringe pattern that consists of a series of bright and dark bands.

Fringe pattern:

• Is a series of bright and dark bands that is produced by the interference of waves.
• The spacing of the fringes depends on the wavelength of the waves, the distance between the sources, and the distance from the sources to the screen.

Speckled pattern:

• Is a pattern of bright and dark spots that is produced by the interference of incoherent waves.