Phase jump
The phase jump is a physical process in which the phase of a wave changes abruptly. In the picture opposite, the phase jump at A is about 90 °, at B and D each about 180 °.
Phase jumps are important for interference phenomena of different types of waves, especially for the formation of standing waves in closed spaces.
causes
Phase jumps of any value can arise spontaneously in a light source. They occur very frequently in incandescent lamps and very rarely in lasers (see coherence length ).
Phase jumps occur at certain interfaces. If, for example, light that is polarized perpendicular to the plane of incidence is reflected on an optically denser medium or a metal surface , the incident and reflected waves are shifted from one another (λ = wavelength ). This corresponds to a phase shift of . When reflecting on the optically thinner medium, e.g. B. at the transition from glass to air in a prism, however, there is no phase jump.
In the case of a discontinuous change in the wave impedance, for example at the connection point between an electrical line ( coaxial cable ) and an antenna , the same applies.
For quantum mechanical wave functions there is a phase jump from when reflecting on a potential wall.
Phase jump in water waves
In contrast to the almost perfect reflection on a vertical wall (bank wall), in which there is no noticeable phase jump, the size of the phase jump (= phase difference between incident and reflected wave) depends on both the angle of inclination and the surface properties of the wall on inclined bank slopes (inclined walls) as well as the length and height of the waves. Under these circumstances, incident and reflected waves overlap to form partial standing waves ( partial clapotis ). Provided that the bank slopes are relatively steep, the phase jumps become larger the shorter the waves and the lower the slope of the bank. For phase jumps of (180 °) there is a vibration node on the surface of the slope, see the adjacent figure. Phase jumps with (180 °) were determined for level slopes of 1: n ≤ 1: 3 and wave frequencies f ≥ 0.6 Hz. The phase jump also appears as the phase angle of a reflection coefficient defined as complex.
literature
Büsching, Fritz: Phase jump in the partial reflection of irregular water waves on steep embankments , 1. HANSA - International Maritime Journal - C 3503 E, 147, H.5 p.87-98, 2010. 2. INLAND SHIPPING - C 4397 D, 65, H.9 p.73-77 & H.10 p.64-69, 2010.
Büsching, Fritz .: Phase Jump due to Partial Reflection of Irregular Water Waves at Steep Slopes , Coastlab 10, Barcelona, Spain, 28th-30th September, 1st October 2010, Paper No. 67, p.1-9.