how can i find the angle ofdeviation?

Visible light which is also known as white light is the of collection of component colors which are often observed as light passes through a triangular prism.Since on passage through the prism the white light is separated into its component colors - red,orange, yellow,green,blue and violet.Such separation of visible light into its different colors is known as dispersion.
The amount of overall refraction caused by the passage of a light ray through a prism is often expressed in terms of the angle of deviation.It is the angle made between the incident ray of light entering the first face of the prism and the refracted ray that emerges from the second face of the prism.Because of the different amount of refraction for the different wavelengths of visible light,the angle of deviation gets varies with wavelength.Colors of the visible light spectrum which have shorter wavelengths(VIB will deviated more from their original path than the colors with longer wavelengths (YOR).

Approved

Dear student i am explaining you how the angle of deviation can be found.You will surely understand how to find the angle of deviation.Allk the best.
Le us suppose a ray KL is incident on the face AB of the prism at the point F( for the figure see below) where N1LO is the normal and∠i1is the angle of incidence.Since the refraction takes place from air to glass, therefore,the refracted ray LM bends toward the normal such that∠r1is the angle of refraction.Ifµ be the refractive index of glass with respect to air, then
µ = sin i/sin r ------- (By Snell’s law)
The refracted ray LM is incident on the face AC at the point M where N2MO is the normal and∠r2is the angle of incidence.Since the refraction now takes place from denser to rarer medium, therefore,the emergent ray MN such that∠i2is the angle of emergence.Now in the absence of the prism,the incident ray KL would have proceeded straight, but due to refraction through the prism,it changes its path along the direction PMN. Thus,∠QPN gives the angle of deviation ‘δ’, i.e. the angle through which the incident ray gets deviated in passing through the prism.
Thus, δ = i1– r1+ i2-r2 ….... (1)
δ = i1+ i2– (r1+r2)
Again, in quadrilateral ALOM,
∠ALO +∠AMO = 2rt∠s [Since,∠ALO = ∠AMO = 90º]
So,∠LAM +∠LOM =2rt∠s [Since, Sum of four ∠s of a quadrilateral = 4 rt∠s] ….... (2)
Also in?LOM,
∠r1+∠r2+∠LOM = 2rt∠s …... (3)
Comparing (2) and (3), we get
∠LAM =∠r1+∠r2
A =∠r1+∠r2
Using this value of∠A, equation (1) becomes,
δ = i1+ i2- A
ori1+ i2=A +δ …... (4)
This is how the angle of deviation can be found

Thanks dear.