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TWO-SOURCE INTERFERENCE
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TWO-SOURCE INTERFERENCE OF WAVES

State the conditions necessary to observe interference between two sources.
PHET WAVE INTERFERENCE SIMULATION investigate the conditions for interference at the PHET website.
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Explain, by means of the principle of superposition, the interference pattern produced by waves from two coherent point sources.

SUPERPOSITION: When two waves pass the same point at the same time, their displacements are added together to calculate the resultant displacement.
COHERENT: Sources of waves with the same frequency, similar amplitude and constant phase difference are coherent.
CONSTRUCTIVE INTERFERENCE: When two coherent sources, which are in phase, superpose, they add to give a wave of double amplitude. Also called Reinforcement.
DESTRUCTIVE INTERFERENCE: When two coherent sources, which are out of phase, superpose, they add to give a wave of zero amplitude. Also called Cancellation.


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The effect may be illustrated using water waves and sound waves in addition to EM waves.


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Outline a double-slit experiment for light and draw the intensity distribution of the observed fringe pattern.

DOUBLE SLIT EXPERIMENT: Light from two point sources interfere and cause a pattern of fringes caused by constructive and destructive superposition.
PATH DIFFERENCE: The distance, measured in wavelengths, between the paths taken by 2 waves.




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This should be restricted to the situation where the slit width is small compared to the slit separation so that diffraction effects of a single slit on the pattern are not considered.

Solve problems involving two-source interference.
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from IB formula book

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