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#wave model

3 public questions tagged with this topic.

What ensures that the laws of reflection hold true when derived using the wave model?

**Wavefront types** point source spherical, distant point source plane, after convex lens plane wave focuses to point because lens adds phase delay proportional to thickness, converging spherical wavefront, after concave mirror plane wave becomes spherical converging to focus, illustrating Huygens construction. The wave model uses secondary wavelets, where the reflected wavefront’s envelope forms when the incident and reflected angles are equal, satisfying geometric congruence. Using Δ = d sinθ, y = n λ D/d, a sinθ = n λ, I = I₀ cos²θ, n = c/v, sinC = 1/n, λ' = λ/n and A = 2a cos(φ/2), calcula

Ref: NCERT > Physics Book > Wave Optics > Wavefront and Huygens Principle

Why does the wave model predict that light bends away from the normal when entering a rarer medium?

**Convex lens focusing** plane wave into point because lens introduces phase delay proportional to thickness, converting plane wavefront to spherical converging to focal point, property ensures rays parallel to axis meet at focus, spherical aberration minimized for paraxial rays, lensmaker's formula determines focal length. In a rarer medium, light speeds up, causing the wavefront to tilt away from the normal as it takes less time to travel a longer path. Using Δ = d sinθ, y = n λ D/d, a sinθ = n λ, I = I₀ cos²θ, n = c/v, sinC = 1/n, λ' = λ/n and A = 2a cos(φ/2), calculation gives

Ref: NCERT > Physics Book > Wave Optics > Optical Phenomena and Applications

Why is the backwave not observed in the reflection of light according to the wave model?

The wave model assumes the amplitude of secondary wavelets is zero in the backward direction, though this is an ad-hoc assumption later justified by advanced wave theory.

Ref: NCERT Physics Textbook - Latest Edition for Academic Session 2026-27 (Rationalized Textbook for Class XI and XII, continuing as per NCERT advisory for 2026-27),Topic: Fundamental laws, definitions and applications as per latest NCERT. The section explains governing laws, formulas like μ₀ = 4π.