Definition/Summary
The double slit is a simple configuration used to demonstrate interference effects in waves.

Equations
At distances that are large compared to the spacing between the slits (i.e. the far field), the interference maxima (bright fringes) occur at angles such that
$$d \ \sin\theta \ = \ m \ \lambda$$
where
\begin{align*}d & = \text{the slit spacing (center-to-center)} \\\theta & = \text{the far-field angle} \\m & = \text{(any integer) the order of the }m^{th} \text{ fringe} \\\lambda & = \text{wavelength}\end{align*}
and the minima (dark fringes, or zeroes) occur at
$$d \ \sin\theta \ = \ \left(m+\frac{1}{2}\right) \ \lambda$$
The far-field intensity, as a function of angle, is given by
$$I(\theta) \ = \ 4 I_0 \cdot\cos^2 \delta \cdot\left( \frac{\sin \beta}{\beta} \right)^2$$
where
[tex]\begin{align*}I_0 & = \text{Central peak intensity due...

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