Chapter-9|Ray Optics and Optical Instrument|NCERT 12th Physics:
Prism Formula:
If the angle of incidence is increased gradually, then the angle of deviation first decreases, attains a minimum value(δm) and then again starts increasing.
Note: From graph it is clear that(experimentally).
1. Angle of deviation is minimum for only one value of angle of incidence.
δ→δmin, then i= e and r₁=r₂=r.
2. This is not a parabola.
3. For each δ(except δmin) there are two value of i.
This relation is called a Prism formula.