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Physics

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  • $\begingroup$ Thanks for your quick response! What is the need for a single slit? Non laser light must be directed through a single slit before a double slit, but for what purpose? For example light from a filament lamp has to be directed through a single slit before the double in order for an interference pattern to form, it can't just be directed through a double slit $\endgroup$
    – John
    Commented Apr 20, 2017 at 15:49
  • 2
    $\begingroup$ The single slit is to produce light from a point source and it produces a diffraction pattern which covers the double slit and so both slits act a sources. If the single slit is made wider then the double slit fringes become less distinct. $\endgroup$
    – Farcher
    Commented Apr 20, 2017 at 15:56
  • $\begingroup$ So the single slit is necessary so that the light directed onto the double slits is from a point source. Am I right in thinking that, as we now have a white light point source, the phase difference between the two double slits is constant as a result. $\endgroup$
    – John
    Commented Apr 20, 2017 at 16:08
  • $\begingroup$ And so the single slit does NOT make a light source monochromatic. All frequencies emitted from e.g. a white light bulb still make it through the single slit, and so the interference pattern is a result of all these difference frequencies. $\endgroup$
    – John
    Commented Apr 20, 2017 at 16:12
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    $\begingroup$ Ok then. So is the reason why we can shine a laser directly at the double slits because it acts as a point source? $\endgroup$
    – John
    Commented Apr 20, 2017 at 16:58