Superposition Flashcards
State the Principle of superposition.
The principle of superposition states that when 2 or more waves of the same kind overlap, the resultant displacement at any point at any instant is given by the vector sum of the individual displacements that each individual wave would cause at that point at that instant.
Define interference.
It is the result of superposition of wavetrains from a finite number of coherent sources.
Define coherence.
It is when 2 or more waves or sources have a constant phase difference
Define path difference.
It is the extra length that the wave from 1 source must travel compared to another source, in order to reach the point of observation.
Define diffraction.
Diffraction is the spreading out of a wave after passing through a slit or around an obstacle.
State the formulae for double slit experiment, single slit experiment, and diffraction grating experiment.
Double slit experiment:
λ = ax/D
a = slit seperation, x = fringe seperation, D = distance between slit and screen, λ = wavelength
Single slit experiment:
sin θ = λ/b
θ = angular displacement from centre of source to the minima of the central fringe, λ = wavelength, b = length of slit opening
Diffraction grating:
d sin θn = nλ
d = slit seperation, θn = angular displacement from centre of source to nth bright fringe, n = non-zero integer, λ = wavelength
State Rayleigh’s Criterion.
It states that the images of two point sources are just resolved when the central maximum of one image falls on the first minimum of the other image.
Define a stationary wave.
When 2 identical of the same amplitude, frequency and speed but travelling in the opposite directions are superposed together, the resultant wave is called a stationary wave.
Define a node.
A node is a location in a stationary wave where the
particles no longer oscillate, typically when two waves
reach the point π radians out of phase.
State 3 conditions for observable interference.
- Overlapping waves must be coherent.
- The waves should have similar amplitudes.
- If they are transverse waves, they must be either unpolarised or polarised in the same plane.
Define an antinode.
An antinode is a location in a stationary wave where
the particles oscillate with the maximum displacement,
typically when two waves reach the point in phase.
Define a fringe.
A Fringe is a location at which constructive (bright fringe) or destructive (dark fringe) interference can be observed.
Define destructive interference.
Destructive Interference occurs when two coherent waves reach a point with a phase difference of π radians to form a resultant minimum displacement.
Define constructive interference.
Destructive Interference occurs when two coherent waves reach a point in phase to form a resultant maximum displacement.
