Refraction of a plane wave into a rarer medium (bends away from the normal)विरल माध्यम में समतल तरंग का अपवर्तन (अभिलंब से दूर)Refraction of a plane wave into a rarer medium (bends away from the normal)
NCERT Fig 10.5 · Class 12 Physics · Chapter 10 · interactive diagram
Parts and what they mean
- Incident wavefront AB (आपतित तरंगाग्र AB) — A plane wavefront arriving at angle i. When end A touches the surface, end B still has distance BC to go.
- BC = v₁τ (BC = v₁τ) — In time τ the disturbance from B travels to C at speed v₁ in medium 1.
- Secondary wavelet from A (A से द्वितीयक तरंगिका) — In the same time τ the wavelet from A spreads into medium 2 with speed v₂, radius AE = v₂τ.
- AE = v₂τ (AE = v₂τ) — Radius of the wavelet; AE is also the refracted ray through A (it is perpendicular to CE).
- Refracted wavefront CE (अपवर्तित तरंगाग्र CE) — Tangent plane drawn from C to the wavelet. From triangles ABC and AEC: sin i = v₁τ/AC, sin r = v₂τ/AC ⇒ sin i / sin r = v₁/v₂ = n₂/n₁ (Snell’s law).
- Angle of incidence i (आपतन कोण i) — Angle between the incident ray and the normal (equal to the angle between wavefront AB and the surface).
- Angle of refraction r (अपवर्तन कोण r) — Here v₂ > v₁, so r > i: the ray bends away from the normal. If sin i = n₂/n₁ (critical angle) then r = 90°; beyond it there is no refracted wave — total internal reflection.
- Incident rays (आपतित किरणें) — Perpendicular to the incident wavefront.
- Refracted rays (अपवर्तित किरणें) — Perpendicular to the refracted wavefront CE.
- Normals (अभिलंब) — Lines perpendicular to the surface; angles are measured from them.
- Surface PP′ (पृष्ठ PP′) — Boundary separating medium 1 and medium 2.
- Medium 2 (माध्यम 2) — Optically rarer here (e.g. air below water): speed v₂ > v₁.
Original diagram drawn by Simple Learning Hub, based on NCERT Fig 10.5. Report a mistake