Ch 9 covers ray optics comprehensively — reflection/refraction at surfaces, total internal reflection, prism dispersion, thin lens formula, and optical instruments (microscope, telescope).
Snell's law: n₁ sinθ₁ = n₂ sinθ₂. Total internal reflection: when light goes from denser to rarer medium at angle > critical angle. sinθ_c = n₂/n₁. Applications: optical fibres (communication), mirage. Prism: δ = (i₁ + i₂) − A; at minimum deviation D_m: n = sin((A+D_m)/2)/sin(A/2).
Lens maker's equation: 1/f = (n−1)(1/R₁ − 1/R₂). Power P = 1/f. Combinations: P = P₁ + P₂. Compound microscope: objective (short f, real inverted image) + eyepiece (magnifies). Magnification ≈ −L/f_o × D/f_e. Astronomical telescope: objective (large f, captures light) + eyepiece. m = −f_o/f_e. Length = f_o + f_e.
Download: https://ncert.nic.in/textbook/pdf/leph201.pdf | Part II: https://ncert.nic.in/textbook/pdf/leph2ps.zip
An optical fibre has a glass/plastic core with a higher refractive index surrounded by cladding of lower refractive index. Light enters at one end and undergoes repeated total internal reflection at the core-cladding boundary, travelling through the fibre with minimal loss even around bends. This principle enables high-speed data communication over long distances.
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