Flashcards · 7408 · Topic 3

Waves flashcards

15 cards on Topic 3, subtopics 3.3.1 to 3.3.2. Pick a subtopic or study them all.

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Wavelength (of a progressive wave): The distance between adjacent points in phase.
Phase difference: How far one point is ahead of another in its cycle, as a fraction of a cycle, in degrees or in radians: ¼ cycle = 90° = π/2 rad; ½ cycle = 180° = π rad.
Transverse vs longitudinal waves, and what polarisation shows: Transverse: oscillation perpendicular to the direction of energy transfer (all EM waves). Longitudinal: parallel (sound). Only transverse waves can be polarised, so polarisation is evidence that a wave is transverse.
How is a stationary wave formed?: Two progressive waves of the same frequency travelling in opposite directions (often a wave and its reflection) superpose. Nodes form where they are always in antiphase, antinodes where always in phase.
Progressive vs stationary wave: energy, amplitude and phase: Progressive: transfers energy; same amplitude everywhere; phase changes continuously along the wave. Stationary: stores energy; zero at nodes, maximum at antinodes; same phase within a loop, antiphase in adjacent loops.
Distance between adjacent nodes of a stationary wave: λ/2. Count the gaps between nodes, not the nodes.
First harmonic on a string: the equation, and the effect of quadrupling the tension: f = (1/2l)√(T/μ), where μ is mass per unit length. f ∝ √T, so quadrupling T doubles f.

Coherent sources: Same frequency and a constant phase difference.
Young's double slits: λ = 600 nm, D = 2.0 m, s = 0.50 mm. Find the fringe spacing.: w = λD/s = (6.0 × 10⁻⁷ × 2.0) ÷ (5.0 × 10⁻⁴) = 2.4 × 10⁻³ m = 2.4 mm.
Diffraction grating equation, and how to find the highest order: d sin θ = nλ, with d = 1 ÷ (lines per metre). Highest order = the largest whole number ≤ d/λ (round down).
Single-slit diffraction: the pattern, and what makes the central maximum wider: A bright central maximum twice the width of the dimmer side maxima. It is wider if the wavelength increases or the slit width decreases.
Conditions for total internal reflection, and the critical angle equation: Light travels from higher to lower refractive index (n₁ > n₂) at an angle of incidence greater than the critical angle. sin θc = n₂/n₁.
Cladding of an optical fibre: why is it used?: It has a lower refractive index than the core (allowing TIR), protects the core from scratches, and stops crossover of signals between fibres.
Material dispersion vs modal dispersion in a fibre, with the fix for each: Material: different wavelengths travel at different speeds; fix with a monochromatic source. Modal: rays take different paths of different lengths; fix with a very narrow (single-mode) core.
Double-slit fringes with white light: A white central fringe; the other fringes are coloured, with blue nearer the centre.