Wize University Physics Textbook (Master) > Wave Optics
Realistic Double Slit diffraction
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Realistic Double Slits
In real life, the two slits are never infinitely thin (they are not really point sources), they actually have a width.
- This means that each of the two slits will generate a single-slit diffraction pattern.
- The result is that we have a single-slit envelope with the pattern of dark and bright fringes from the actual two-slit interference contained inside each bright region.
- To get information about the distance between the two slits, you have to look at peaks generated by the double slit pattern (the narrow bright spots).
- To get information about the size or width of each slit, you have to look at the position of the first minimums for the bigger pattern where the central max of the envelope dies off.
Wize Concept
- We can see the single-slit envelope much better if the width of the slits is comparable to the distance between them.
- If the width of the lists is much smaller than the distance between them, the envelope is so spread out that we can't distinguish this single-slit pattern and we only see the fringes inside (from the double-slit interference).
Practice: Realistic Double Slits
The intensity pattern of a double-slit configuration at m is shown below.
The horizontal axis shows the displacement in mm. The wavelength is nm.
a) Find the angle from the center of slits at which the first spectral order maximum happens.
b) What is the distance between the two slits?
c) What is the width of each slit?
