#light waves

Optical Phenomena and Applications

What property of light waves is responsible for the redistribution of energy into bright and dark regions during diffrac

**Polarization requires transverse waves** because only transverse can have orientation perpendicular to propagation, longitudinal cannot be polarized, wave theory requires light transverse to explain polarization, polaroids transmit only component along pass-axis, unpolarized has random transverse orientations, after polaroid polarized. The superposition of secondary wavelets causes constructive and destructive interference, redistributing energy into bright and dark regions. 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), calculat

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

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Wavefront and Huygens Principle

What property of light waves enables the formation of a stable interference pattern when split from a single source?

**Wavefront** is locus of points in same phase, spherical from point source, plane at large distance because radius large, Huygens principle every point on wavefront acts as secondary source of wavelets, new wavefront envelope of secondary wavelets, allows prediction of new wavefront shape from known wavefront, explains reflection and refraction. Coherence, or a fixed phase relationship, is maintained when light from one source is split, allowing constructive and destructive interference to form a stable pattern. Using Δ = d sinθ, y = n λ D/d, a sinθ = n λ, I = I₀ cos²θ, n = c/v, sinC = 1/n, λ

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

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Wave Properties, Frequency and Energy Conservation

What property of light waves explains why the frequency remains constant when light refracts into a denser medium?

**Frequency of light** remains unchanged when refracts from air into water because frequency determined by source, energy E= h f conserved, speed decreases v= c/n, wavelength decreases λ'=v/f= λ/n, energy of wave proportional to amplitude² not speed, intensity I =½ c ε₀ E₀², energy not depend on speed directly, when speed decreases amplitude may change but energy conserved, interference redistributes energy, total energy same, bright regions gain from dark. Frequency is determined by the source and remains unchanged, while speed and wavelength adjust to the medium’s properties. Using Δ = d sin

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

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Polarization and Malus Law

What is the nature of light waves demonstrated by polarization?

**Two polaroids** with pass-axes perpendicular intensity zero because second blocks component, with 45° intensity I₀/4 if initial after first I₀, if initial unpolarized I₀, after first I₀/2 then after second at 45° I₀/4. Three polaroids first and third crossed 90°, middle at 45° maximum transmission because middle rotates polarization, I after first I₀/2, after middle at 45° I₀/4, after third at 45° to middle I₀/4×cos²45°= I₀/8, non-zero, maximum when middle 45°. Polarization shows that light waves are transverse, as only transverse waves can be polarized. Using Δ = d sinθ, y = n λ D/d, a sinθ

Ref: NCERT > Physics Book > Wave Optics > Polarization and Malus Law

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