Physics · Ch 6 — Optics
Angle of Minimum Deviation
Angle of Minimum Deviation
Plotting the angle of deviation against the angle of incidence for a prism gives a curve that falls to a single minimum value , called the angle of minimum deviation, before rising again on either side. At this minimum: (a) the angle of incidence equals the angle of emergence, ; (b) the two internal refraction angles are equal, ; (c) the incident and emergent rays are symmetrical with respect to the prism; and …
What this figure shows. A plot of the angle of deviation d against the angle of incidence i for light passing through a prism shows a curve that falls from a large value at grazing (near-90-degree) incidence, down through a single minimum, and then rises again as incidence approaches grazing on the other extreme -- the curve's one and only minimum point is the angle of minimum deviation D, the key quantity used to determine a pri …
What this figure shows. The ray path through a prism at exactly minimum deviation is shown symmetric about the prism's own bisector: the incidence angle i on the first face exactly equals the emergence angle i on the second face, and correspondingly the two internal refraction angles r are also equal to each other, with the internal ray segment running parallel to the prism's base -- this symmetric geometric picture is what lets i1 = i2 = i and r1 = r2 = A/2 be substituted directly into the general deviation …