A-Level Physics · Topic 4
Waves and optics: every key term you need (+ practice quiz)
16 flashcard terms for A-Level Physics Topic 4, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
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Progressive vs stationary wave A progressive wave transfers energy; a stationary wave stores it, formed by superposition of two identical waves travelling in opposite directions.
Node and antinode On a stationary wave, a node has zero amplitude from destructive interference; an antinode has maximum amplitude from constructive interference.
Transverse vs longitudinal Transverse oscillations are perpendicular to energy transfer and can be polarised; longitudinal oscillations are parallel and cannot.
Polarisation Restricting oscillations to one plane. Only transverse waves polarise, which is how we know light is transverse.
Phase difference How far through their cycles two oscillations are relative to each other, measured in radians or degrees.
Coherence Two sources are coherent if they have the same frequency and a constant phase difference — required for a stable interference pattern.
Path difference The extra distance travelled by one wave. Whole wavelengths give constructive interference, odd half wavelengths destructive.
Young's double slit Two coherent sources produce evenly spaced fringes. Fringe spacing equals wavelength times slit-to-screen distance divided by slit separation.
Diffraction grating Many slits give sharper, brighter maxima than a double slit, so wavelength can be measured far more precisely.
Single slit diffraction Produces a wide central maximum twice the width of the others. Narrowing the slit widens the pattern.
Refractive index The ratio of the speed of light in a vacuum to its speed in the medium. Always greater than one, and has no units.
Snell's law Relates the angles of incidence and refraction to the refractive indices of the two media at the boundary.
Total internal reflection Occurs when light travelling into a less dense medium meets the boundary above the critical angle. The basis of optical fibres.
Optical fibre cladding Lower refractive index than the core, so light totally internally reflects. It also prevents signal crossover and protects the core.
Modal dispersion Rays taking different paths arrive at different times, spreading the pulse. Reduced by a narrower core.
Harmonics on a string The fundamental has one antinode. Each successive harmonic adds a node, so frequencies are whole-number multiples of the fundamental.
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