University of St Andrews
School of Physics and Astronomy

11.  Two-beam interference via Phasors

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Associated tutorial questions (St Andrews only)

• Two beam interference can be looked at quantitatively using phasor diagrams
• Recap on what a phasor is.
• Adding phasors is done in the same way as adding vectors.
• We find that the intensity of a wave is proportional to the length of the resultant phasor.
• For a given phase difference between two phasors we can draw the vector diagram (phasor addition) to analyse the situtation.
• For two beam interference we find exactly the same answer for the intensity variation with phase difference as we did in the last lecture algebraically.
• We will also consider temporal and spatial coherence and their relevance to interference patterns.

Similar material to that presented in the lectures is available at:-

• Halliday, Resnick, & Walker - Chapters on:-  Interference

Associated tutorial questions (St Andrews only)
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Created by, and copyright of, Bruce Sinclair, University of St Andrews; last modified 18/09/01