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Module 4 - Chapter 12 - Waves 2 I - Coggle Diagram
Module 4 - Chapter 12 - Waves 2 I
Superposition
Surposition happens when waves overlap to produce a single wave who instantaneous displacement can be found using the principle of superposition of waves
Principle of superposition - when two waves meet at a point, the resultant displacement at that point equals the sum of the displacement of the individual waves
Superposition to interference
Interference is when two progressive waves continuously pass through each other and superpose to produce a resultant wave
If two waves are in phase, maximum positive displacements line up, creating a resultant displacement with increasing amplitude (constructive intereference)
Increasing amplitude increases the intensity as
If two waves are in antiphase, maximum positive displacement of one lines with maximum negative displacement of another, resultant displacement is smaller than for each wave (destructive interference)
Waves with same amplitude will have zero amplitude after destructive interference
When 2 progressive waves of the same frequency are travelling in opposite directions in the same medium, they superpose
Interference
Stable interference pattern
Coherence - waves emitted from two sources having a constant phase difference
To be coherent, waves must have the same frequency and phase difference
Interference is the superposition occuring between two coherent waves
Path/phase difference
Interference patters contain a series of maxima/ minima
Maximum - waves interferece constructively
Minimum - interfere destructively
Maxima and minima are result of wave having travelled different distances from their sources (path difference)
If the path difference to a point is 0 or a whole number of wavelengths. two wave will always arrive at a point in phase - constructive interference
If the path difference to a point is an odd number of half wavelengths, two wave will always meet at anti phase - destructive interference
At central maxima, path difference is zero, so phase difference is zero - constructive interference
First order maxima, path difference is one whole wavelength, phase difference is 360 - constructive interference
First order minima - path difference is half a wavelength, phase difference is 180 - destructive interference
Sound
Two loudspeaker connected to the same signal generator emit coherent sound waves
Sounds waves overlap and form an interference pattern
Pattern comprises of a series of maxima (louder) and minima (softer)
Detect using ears ofa microphone
Microwaves
Single microwave source is used with a pair of slits
Diffracted microwaves overlap, forming an interference pattern that can be detected with a microwave receiver connected to a voltmeter/ oscilloscpoe
Moving a receiver in an arc around the double slit detects the characteristic maxima/ minima
Diffracted waves are coherent
Young double-slit experiment
Experiment
Two coherent waves are needed to form an interference pattern
A monochromatic source of light must be used, you can create this using a colour filter
Light differactng front the single slit arrives at the double slit in phase, and then diffracts again from the double slit
Each slit is a source of coherent waves, which spread and overlap to form an interference pattern on a screen of alternating light/dark regions called fringes
Demonstrates the wave nature of light
Equation
Separation between slits in a (S1-S2)
Distance between the screen and slits in D, D > a
Separation between finges is x (X-Y)
Path difference must be equal to one whole wavelength
Distance between the slits is much smaller than the distance from the screen to the double slits
and
Diffraction grating
Piece of transparent material with many opaque lines scratched into it
Light can pass through the transparent slit between scratches, and produce an interference paaterin with bright and dark minima/maxima
Order of maxima is the angle between the 0th and nth maxima
Adjustments
If the amplitude of the two waves increases, bright fringes have a higher intensity
If one of the waves was made 180 degrees out of phase, bright fringes would be converted to dark fringes
