INTERFERENCE PATTERNS
A system with two point sources can be set up in a ripple tank, with dippers vibrating in and out of the water, or with sound waves, by having two speakers wired to a frequenct generator. When using light waves a double slitted gobo is used so that both waves come from the same source. The diagram shows the type of pattern that is produced, the blue lines, represent the crests from one source and the red from the other. The black lines show where there is most constructive interference . Inbetween there will be a point of minimum (zero if amplitudes are equal) displacement.

Notes:

• To observe any interference pattern the waves must be coherent.
• Coherent means that there is a constant phase difference between them and they are vibrating in the same plane.