Interference and diffractionPhase difference and coherenceIf two harmonic waves of frequency and wavelength gelombamng same but different phase, a wave that produced a harmonic wave is dependent on the phase. If the phase difference 0 or an integer multiple of 3600, the wave phase and berinterfensi will be mutually reinforcing. Summing the amplitudes equal to the amplitude of each, and its intensity (which is proportional to the square of the amplitude)'s maximum. If the phase difference 1800 (π radians) or an odd number times 1800, waves of different phase and will interfere with each other secar debilitating. The resulting amplitude is thus a difference in their amplitude, and intensity to a minimum. If the amplitude is the same, intesitasnya to a maximum equal to 4 times the minimum inensitasnya equal to zero.The cause of the phase difference between the two waves is the 1800 phase changes that are sometimes experienced by the current wave reflected from the surface of the bats.This phase change analogous to the inverse pulse on the thread, when the pulse was bounced from a point where the density is suddenly increased, as when a small thread in the threads that connect to a greater or rope. Inverse the reflected pulse is equivalent to the phase change 1800 to sinusoidal waves, which can be viewed as a pulse train. When light propagates through the air on the surface of the medium in which light will propagate more slowly, such as glass or water, there will be changes to the 1800 phase of the reflected light tone aka phase changes in the reflected light from the surface of the glass-air or water -air. This is analogous to the inverse reflectance without a pulse on the yarn thickness at the point where the thick yarn in conjunction with fine threads.Phase difference between the two waves is also often caused by differences in path length traveled by the wave kadua. One wavelength path difference leads to different phases of 3600, which is equivalent to no phase difference at all. Perbaan trajectory detengah wavelength produces a phase difference of 1800. Generally the same path difference Δr accounts for a phase difference δ that is given is:δ = (Δr) / λ 2 π = (Δr) / λ ^ 0 〖360〗Gelobang interference from the two sources did not observed unless the source is coherent, that is, except for the phase difference between the wave is constant over time.Because the light beam pa generally is the result of millions of atoms radiate independently, the two light sources are usually not coherent. Indeed, the phase difference between waves from such sources fluctuate randomly several times per second.Coherence in optics is often achieved by dividing the light from a single source into two result in interference pattern. Pembagiaan This can be achieved by reflecting light from two separate meetings on the surface of a thin film (Article 33-2): simultaneous reflection from and propagation through a glass-coated side, as in the Michelson interferometer