What is the Double Slit? A 5 Minute Introduction

[Greg Bernhardt]

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
\begin{align*}I_0 & = \text{Central peak intensity due...

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