This is a very basic question, but I just forgot how to solve this. It's classical physics question.

Suppose that there are two light sources. And some place away exists a screen. How do I find maximum light intensity points and minimum light intensity points?

And what is the process behind this?

BTW, I assume equal frequency, amplitude and power for all sources

  • $\begingroup$ This questions skates right along the thin line between "basic exercises" which are forbidden by the FAQ and "basic conceptual questions" which are allowed. Future respondents should stick to conceptual notes in the mode of John's answer. $\endgroup$ – dmckee --- ex-moderator kitten Jun 1 '12 at 13:07

Suppose your sources are at points $A$ and $B$ and you're calculating the intensity at point $C$. Calculate the two distances $AC$ and $AB$. If the difference between these two distances is an integral number of wavelengths the two waves will be in phase at the point $C$ and will add to each other so you get a bright spot. If the difference $AC - BC$ at the point $C$ is a half integral number of wavelengths the two waves will be out of phase and will cancel each other out and you'll get a dark spot.

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    $\begingroup$ You also have to assume that the light sources are coherent. The phrasing of the question makes me think the OP was imagining something like light bulbs shining on a screen, which wouldn't lead to a stable interference pattern because the light bulbs (or even LEDs) emit incoherently. $\endgroup$ – kleingordon Jun 1 '12 at 8:21

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