Angle of Deviation
The angle between the direction of an incident light ray entering an optical element (like a prism) and its emerging direction.
Governing formula
δ = i1 + i2 - A
SI unit
Degrees (°)
In depth
In a triangular prism, deviation $Δ$ depends on incidence angle $i_1$, prism refracting angle $A$, and material refractive index $n$.
Examples in the real world
Measuring deviation angle $Δ$ of a light ray passing through a glass triangular prism in a spectrometer.