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#optics fundamentals

3 public questions tagged with this topic.

Wave Properties, Frequency and Energy Conservation

What ensures that light rays appear to travel in straight lines despite their wave nature?

**Intensity not depend on speed** when enters denser medium because intensity I ∝ n E₀²? Actually Poynting vector S = E×H, energy density u =½ ε E², for same amplitude E₀ intensity proportional to n, but amplitude changes at interface due to reflection, total energy conserved incident = reflected + transmitted, interference does not destroy energy, it redistributes. The extremely small wavelength of light compared to everyday objects minimizes wave effects, making rectilinear propagation dominant in macroscopic observations. Using Δ = d sinθ, y = n λ D/d, a sinθ = n λ, I = I₀ cos²θ, n = c/v, s

Ref: NCERT > Physics Book > Wave Optics > Wave Properties, Frequency and Energy Conservation

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Refraction, Refractive Index and Critical Angle

What determines the intensity of light in the wave picture?

**Refractive index** n = c/v, c=3×10⁸ m/s vacuum, v speed in medium, for v=2.25×10⁸ m/s n=3/2.25=1.33, for v=1.8×10⁸ n=1.67, for n=1.3 v=3×10⁸/1.3=2.31×10⁸ m/s, for n=1.6 v=1.875×10⁸ m/s, for n=1.2 λ_medium = λ_vacuum/n =600/1.2=500 nm, for n=1.75 λ=700/1.75=400 nm, for n=1.5 λ=750/1.5=500 nm, wavelength in medium λ' = λ/n. In the wave picture, intensity is proportional to the square of the amplitude of the wave. 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 Square of the amplitude, illustrating interference, dif

Ref: NCERT > Physics Book > Wave Optics > Refraction, Refractive Index and Critical Angle

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Wavefront and Huygens Principle

What is the shape of the wavefront after a plane wave reflects off a plane mirror?

**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. A plane wave reflecting off a plane mirror remains a plane wavefront, as the reflection preserves its flat nature. 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 Plane, illustrating interference, diffractio

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

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