Stationary Waves and Diffraction (Physics - Secondary 6)

Vocabulary flashcards covering stationary waves, harmonics, interference, and diffraction concepts from the notes.

Stationary waves (standing waves)

Waves formed by the superposition of two waves of equal frequency and amplitude traveling in opposite directions, producing a pattern with fixed nodes and antinodes where energy is stored.

Superposition principle

The resultant displacement at a point is the sum of the displacements of each incoming wave.

Constructive interference

Waves in phase; peaks and troughs align, giving a larger resultant amplitude.

Destructive interference

Waves out of phase; peaks align with troughs, reducing or canceling the resultant amplitude.

Node

Point on a stationary wave with zero displacement (no vibration).

Antinode

Point on a stationary wave with maximum displacement.

Phase difference

The offset in phase between two points on a wave; between nodes points are in phase, across a node they are out of phase.

Progressive (travelling) wave

A wave that transfers energy through a medium and has a moving pattern.

Energy transfer vs energy storage

Progressive waves transfer energy; stationary waves store energy.

Boundary condition: fixed end

End of a string anchored in place, creating a node at the boundary.

First harmonic (fundamental) on a string

Lowest-frequency standing wave with one loop; λ1 = 2L and f1 = v/(2L).

Wavelength of first harmonic

λ1 = 2L for a string of length L fixed at both ends.

Frequency of first harmonic

f1 = v/(2L), where v is the wave speed on the string.

Velocity on a string

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

Second harmonic

Standing wave with two loops; λ2 = L and f2 = 2f1.

Third harmonic

Standing wave with three loops; λ3 = 2L/3 and f3 = 3f1.

Wavelength of second harmonic

λ2 = L.

Wavelength of third harmonic

λ3 = 2L/3.

Diffraction

Spreading out of waves as they pass an obstacle or through an aperture.

Single slit diffraction

Diffraction pattern from a narrow slit: central maximum with equally spaced, smaller subsidiary maxima.

Central maximum

The brightest central fringe of a diffraction pattern.

Minima condition (single slit)

For slit width a, minima occur when a sin θ = mλ (m = ±1, ±2, …).

Diffraction grating

A plate with many parallel slits that produces sharp bright fringes by constructive interference.

Grating equation

d sin θ = n λ, where d is slit spacing and n is the order of the maximum.

d (slit spacing)

Spacing between adjacent slits on a diffraction grating; d = 1/N where N is lines per meter.

N (lines per meter)

Number of lines per meter on a diffraction grating; higher N means smaller d.

Applications of diffraction gratings

Used in spectrometers to analyse light from stars, measure wavelengths, and in x-ray crystallography.

X-ray diffraction in crystallography

X-ray wavelengths comparable to atomic spacings; diffraction patterns reveal atomic spacing.

Wavefront

A locus of points that have the same phase; used to visualize diffraction and interference.

Aperture

An opening through which waves pass and diffract.