# ^Deviation of the emergent ray

^**Deviation of the emergent ray**

Incident ray deviates clockwise towards the base at first face by amount δ_{1 }(= i_{1} – r_{1}) & then again deviates clockwise towards the base at second face by amount δ_{2 }(= r_{2} – i_{2}), thus the total deviation of the prism sum of δ_{1} & δ_{2 }. Also from the cyclic quadilaternal AEHF,

r_{1} + i_{2} = A. From this information we can write

δ = δ_{1 }+ δ_{2 }= i_{1} + r_{2} – A [Called Prism equation

For given μ, λ & A with the increase of incidence angle deviation angle first decreases & becomes minimum & then starts increasing as shown in the graph.