A given ray of light suffers minimum deviation in an equilateral prism P. Additional prism Q and R of identical shape and of the same material as P are now added as shown in the figure. The ray will now suffer

Concept :

When a light ray suffers minimum deviation in a prism, the angle of incidence and the angle of emergence are equal, and the light ray travels symmetrically through the prism. When additional prisms of identical shape and material are added in such a way that the light ray enters and exits at the same angle, the overall deviation remains unchanged.

Calculation:

Given that the prism P causes the ray to suffer minimum deviation:

⇒ Deviation in prism P = δ_min

When additional prisms Q and R are added:

⇒ Deviation in prism Q and R = 0 (since they are identical and arranged symmetrically)

Total deviation = Deviation in P + Deviation in Q + Deviation in R

⇒ Total deviation = δ_min + 0 + 0

∴ Total deviation = δ_min

Hence, the ray will now suffer the same deviation as before.