Waves and Optics - Vocabulary Flashcards

Vocabulary flashcards covering key concepts from the lecture notes on waves, interference, diffraction, polarization, and related topics.

Wave

A traveling disturbance in a medium that transfers energy from one place to another.

Progressive wave

A wave that transfers energy along the direction of its motion.

Mechanical wave

Waves that require a medium to travel (e.g., earthquakes, sound, water waves).

Electromagnetic wave

Waves that do not require a medium and can travel through vacuum (e.g., light, microwaves, gamma rays).

Source

The origin from which a wave or disturbance starts.

Medium

Substance through which a wave travels.

Vibration

Oscillation about a fixed position.

Oscillation

Repeated motion around an equilibrium position.

Crest

The highest point of a transverse wave.

Trough

The lowest point of a transverse wave.

Wavelength (λ)

Distance between consecutive points in phase on a wave.

Time period (T)

Time taken to complete one full cycle of a wave; units: seconds.

Frequency (f)

Number of cycles (or waves) per unit time; units: Hz.

Wave speed (v)

Speed of a wave; v = fλ.

Displacement (x)

Shortest directed distance of a point on a wave from its equilibrium position.

Amplitude (A)

Maximum displacement of a particle from its equilibrium.

Equilibrium/rest position

The position where a vibrating particle would stay if undisturbed.

Phase angle (φ)

Angle representing the relative position in a cycle between points or waves; measured in degrees or radians.

In phase

Two points or waves whose phase difference is 0° (or multiples of 360°).

Anti-phase

Two points with a phase difference of 180° (π radians).

Phase difference

Difference in phase between two points on a wave or between two waves.

Transverse wave

A wave where particle vibration is perpendicular to the direction of travel (crest and trough).

Longitudinal wave

A wave where particle vibration is parallel to the direction of travel (compressions and rarefactions).

Rarefaction

Region of low pressure and low particle density in a longitudinal wave.

Compression

Region of high pressure and high particle density in a longitudinal wave.

Plane of polarization

The single plane in which the vibration of a polarized wave occurs.

Polarization

Process by which a wave is confined to vibrate in a single plane.

Unpolarized light

Light with vibrations occurring in many planes.

Polarized light

Light with vibrations confined to a single plane.

Polarizer (Polaroid)

A device that filters light to have vibrations in a single plane.

Wavefront

Lines that pass through points that are in phase; a convenient way to represent a wave.

Coherent waves

Waves with constant phase angle, same frequency and wavelength (usually from a single source).

Interference

Superposition of waves from coherent sources; results in constructive or destructive outcomes.

Constructive interference

Waves add in phase (crests meet crests, troughs meet troughs) giving maximum displacement.

Destructive interference

Waves subtract out of phase (crest meets trough) giving minimum displacement.

Path difference

Difference in distance traveled by two waves from their sources to a point.

Bright fringe

Result of constructive interference in a double-slit setup; a bright band on a screen.

Dark fringe

Result of destructive interference in a double-slit setup; a dark band on a screen.

Fringe separation

Distance between successive bright (or dark) fringes on a screen.

Diffraction

Spreading of a wave around an obstacle or through a slit; speed, frequency and wavelength remain unchanged; amplitude may decrease.

Diffraction pattern

Arrangement of light and dark fringes produced by diffraction.

Diffraction grating

A device with many slits that produces bright and sharp fringes; characterized by lines per mm; spacing d between slits.

nλ = d sin θ

Grating equation relating wavelength, grating spacing, order n and angle θ.

Order of diffraction

An integer n indicating the principal maxima; first order is n=1, etc.

Monochromatic light

Light of a single frequency and wavelength.

Visible spectrum

Range of visible wavelengths approximately 400–700 nm, from violet to red.

Refractive index (n)

n = sin i / sin r = c/v; measures how much a medium slows light relative to vacuum.

Snell's law

n1 sin i = n2 sin r; describes refraction at a boundary between media.

Refraction

Bending of a wave as it passes from one medium to another due to speed change.

Total internal reflection

Complete reflection that occurs when light attempts to move from denser to rarer medium and the incident angle exceeds the critical angle.

Speed of light (c)

Speed of light in vacuum, approximately 3.0 x 10^8 m/s.

Speed of light in a medium (v)

v = c/n; light slows in a medium with refractive index n.

Standing (stationary) waves

Waves of equal frequency and speed traveling in opposite directions that produce nodes and antinodes.

Node

Point on a stationary wave with zero displacement due to destructive interference.

Antinode

Point on a stationary wave with maximum displacement due to constructive interference.

Open-open pipe (standing waves)

Pipe open at both ends; antinodes at both ends; L = nλ/2.

Open-closed pipe (standing waves)

Pipe open at one end and closed at the other; node at closed end and antinode at open end; L = nλ/4 (n odd).

Fundamental frequency (first harmonic)

Lowest frequency at which a standing wave occurs; for strings: f1 = v/(2L); for open-open pipes similar.

Harmonics

Higher standing wave modes; for strings open at both ends: fn = n f1; for open-closed pipes: only odd harmonics with fn = n f1 (n odd).

Wave speed in a string

v = sqrt(T/μ), where T is tension and μ is mass per unit length.

Doppler effect

Apparent change in frequency or wavelength due to relative motion between source and observer.

Monochromatic source (in context of diffraction/ interference)

A source emitting light of a single wavelength and frequency.

when a wave enters a new medium does its frequency change or wavelength

the wavelength changes while the frequency remains the same