AP Physics 2 / Unit 14: Waves, Sound, and Physical Optics
14.8 Double-Slit Interference and Diffraction Gratings
Notes
Bright fringes where the path difference is a whole number of wavelengths: $d\sin\theta=m\lambda$.
- Small angles: $\displaystyle \Delta y=\frac{\lambda L}{d}$.
- Gratings (many slits) give sharp, bright maxima.
Practice
Moving the slits closer together ($d$ smaller) makes the fringes:
$\displaystyle \Delta y\propto\frac{1}{d}$.
Using red light instead of blue makes fringe spacing:
Longer wavelength.
The central bright fringe has path difference:
Equal paths.
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