In a prism, when light is incident at a very small angle, what is the approximate relationship between deviation and the
**Refraction through prism** deviation δ = i+e-A, minimum when i=e, symmetrical path, r₁=r₂=A/2, n = sin[(A+δ_m)/2]/sin(A/2). In water n_rel = n_prism/n_water =1.5/1.33=1.128, so δ_m reduces because relative index lower, new δ_m from formula with n_rel. For a thin prism with a small angle of incidence, the deviation is approximately equal to the product of the prism’s refractive index minus one and the prism angle (D ≈ (n - 1)A). This simplification holds because the angles of refraction are small, minimizing higher-order effects. Substituting values gives Deviation ≈ (n - 1) × prism angle, which matches expected image position and magnification from mirror/lens formula 1/f =
Ref: NCERT > Physics Book > Ray Optics > Refraction Through Prism and Minimum Deviation