Skip to content
Login Register

#optical dispersion

2 public questions tagged with this topic.

Total Internal Reflection and Critical Angle

Why does a convex lens produce chromatic aberration when used with white light?

**TIR application** requires n₁>n₂ and θ₁>C. Critical angle formula derived from Snell's law with θ₂=90°, n₁ sinC = n₂ sin90° = n₂, so sinC = n₂/n₁. For glass-air sinC=1/1.52, C≈41°, for water-air 48.6°, determining cutoff for transmission. Chromatic aberration occurs in a convex lens because different wavelengths of white light refract by different amounts due to the lens material’s varying refractive index for each wavelength. Shorter wavelengths (e.g., blue) focus closer than longer ones (e.g., red), causing color fringing. Substituting values gives Due to wavelength-dependent refraction, which matches expected image position and magnification from mirror/lens formula 1/f = 1/v - 1/u (lens) or 1/f =

Ref: NCERT > Physics Book > Ray Optics > Total Internal Reflection and Critical Angle

View Details
Refraction Through Prism and Minimum Deviation

In a prism, what condition results in the minimum deviation of light?

**Prism minimum deviation** δ_m satisfies n = sin[(A+δ_m)/2]/sin(A/2), A prism angle (degrees), n refractive index, δ_m minimum deviation. For A=60°, n=1.45, sin[(60+δ_m)/2]=1.45×sin30°=0.725, (60+δ_m)/2=46.5°, 60+δ_m=93°, δ_m=33°, illustrating n increase raises δ_m. In a prism, minimum deviation occurs when the angle of incidence equals the angle of emergence. This symmetry ensures the refracted ray inside the prism is parallel to the base, minimizing the deviation angle. Substituting values gives Angle of incidence equals angle of emergence, which matches expected image position and magnification from mirror/lens formula 1/f = 1/v - 1/u (lens) or 1/f = 1/v + 1/u (mirror), confirming sign conventions and refraction principles.

Ref: NCERT > Physics Book > Ray Optics > Refraction Through Prism and Minimum Deviation

View Details