Wave Optics

Vocabulary flashcards covering key terms and definitions from the Wave Optics lecture, including wavefront types, Huygens’ principle, interference, diffraction, and related experimental terminology.

Wave Optics

Branch of physics that studies the behavior of light using its wave nature.

Wave Front

Locus of points in a medium that oscillate in the same phase.

Ray of Light

Imaginary straight line indicating the direction of light propagation and normal to the wave front.

Spherical Wavefront

Wavefront produced by a point source; surfaces of concentric spheres centered on the source.

Converging Spherical Wavefront

Spherical wavefront whose radius decreases toward the observer, e.g., after passing through a convex lens.

Diverging Spherical Wavefront

Spherical wavefront whose radius increases away from the source, e.g., from a concave lens.

Cylindrical Wavefront

Wavefront generated by a linear source such as a tube light; surfaces of coaxial cylinders.

Plane Wavefront

Wavefront formed by parallel rays from a distant source; surfaces are planes.

Huygens’ Principle

Every point on a wavefront acts as a source of secondary wavelets whose envelope gives the new wavefront.

Secondary Wavelet

Small spherical wave produced by each point on a wavefront according to Huygens’ principle.

Snell’s Law

sin i / sin r = n₂⁄n₁; ratio of sines of incidence and refraction angles equals refractive index between two media.

Refractive Index

Constant equal to the ratio of light velocities (or sines) in two media; measures optical density.

Superposition Principle

Resultant displacement at a point equals the vector (algebraic) sum of individual wave displacements.

Interference of Light

Redistribution of light intensity produced when two or more coherent light waves superpose.

Constructive Interference

Superposition where crest overlaps crest (or trough with trough) giving maximum intensity.

Destructive Interference

Superposition where crest overlaps trough, reducing intensity to a minimum.

Coherent Sources

Two light sources emitting waves of same frequency and a constant phase difference.

Coherence

Property of waves that maintain a constant phase relationship while having identical frequency and wavelength.

Path Difference (Δ)

Difference in distances traveled by two waves to reach a common point.

Phase Difference (ϕ)

Relative difference in phase between two waves at a point, often linked to path difference by ϕ = 2πΔ/λ.

Maxima (Bright Fringe)

Points where resultant light intensity is maximum due to constructive interference.

Minima (Dark Fringe)

Points where resultant light intensity is minimum due to destructive interference.

Young’s Double Slit Experiment (YDSE)

Classic demonstration of interference using two narrow, closely spaced slits illuminated by a single source.

Fringe

Alternating bright or dark band formed on a screen in an interference pattern.

Fringe Width (β)

Separation between two successive bright (or dark) fringes; β = λD/d in YDSE.

Sustained Interference

Stable interference pattern where maxima and minima remain fixed over time.

Diffraction of Light

Bending and spreading of light around edges or through small apertures into regions of geometric shadow.

Fresnel Diffraction

Diffraction pattern observed when source or screen is at finite distance, giving spherical wavefronts.

Fraunhofer Diffraction

Diffraction pattern with source and screen effectively at infinity, producing plane wavefronts.

Single Slit Diffraction

Fraunhofer diffraction pattern produced by a solitary narrow slit; central maximum twice width of others.

Principal Maximum

Central and brightest peak in a single-slit diffraction pattern.

Secondary Maximum

Smaller brightness peaks on either side of the principal maximum in single-slit diffraction.

Angular Width of Central Maximum

Total angle between first minima on both sides; 2θ with sin θ = λ/a.

Spectrograph

Instrument that disperses incoming light into its component wavelengths for analysis.

Diffraction Grating

Optical element with many equally spaced parallel slits producing sharp, linearly dispersed spectra.

Slit Spectrometer

Modern spectrograph setup using a narrow entrance slit, collimator, diffraction grating, and detector.

Collimating Mirror/Lens

Optical component that converts divergent light from the slit into parallel beams before dispersion.

Bandwidth (Bright/Dark)

Distance between adjacent bright or dark bands in interference; equal for both in YDSE.

Central Bright Fringe (White Fringe)

In white-light interference, central fringe appearing white due to zero path difference for all colors.

In Young’s Double Slit Experiment, the position y from the central maximum for bright fringes (maxima) is given by y{bright} = \frac{n\lambda D}{d} and for dark fringes (minima) by y{dark} = \frac{(n+0.5)\lambda D}{d}, where n is the fringe order ($$0, \pm