Ch 10 covers the wave nature of light — Huygens' principle, interference (Young's double slit), diffraction (single slit), and polarisation (Brewster, Malus law).
Huygens' principle: each point on a wavefront acts as a source of secondary wavelets. Young's double slit: two coherent sources produce bright and dark fringes. Bright fringe: path difference = nλ. Dark fringe: (2n+1)λ/2. Fringe width β = λD/d. Intensity at any point: I = 4I₀cos²(πyd/λD).
Single slit diffraction: central maximum (2λ/a wide), secondary maxima diminish. First minimum: a sinθ = λ. Limit of resolution: θ_min = 1.22λ/D (Rayleigh criterion). Polarisation proves light is a transverse wave. Malus' law: I = I₀cos²θ. Brewster's law: tanθ_B = n₂/n₁ (reflected light is completely polarised). Polaroid filters: transmit one direction of vibration.
Download: https://ncert.nic.in/textbook/pdf/leph202.pdf | Part II: https://ncert.nic.in/textbook/pdf/leph2ps.zip
Each point within the slit acts as a source of secondary waves (Huygens). These waves interfere with each other: at certain angles, wavelets from different parts of the slit destructively interfere (path difference = nλ), creating dark fringes. The central maximum is brightest and widest. This demonstrates the wave nature of light — waves can bend around obstacles.
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