Year+13+Double+Slit+Interference

**__Double-slit Interference__** By now you will probably be quite familiar with the picture of a wave moving through two narrow pathways, spreading out in a curve (diffraction) and causing constructive and destructive interference.



As you can see in the above image, the two waves combine to make bright (anti-nodes) and dark (nodes) "fringes" (of light or sound).

Yellow represents a crest, red a trough. Where red meets red and yellow meets yellow we have constructive interference: An anti-nodal line. Where red meets yellow and vice versa we have destructive interference: A nodal line.


 * A wave goes through a small slit (compared to wavelength) and the wave spreads out in a curve.
 * Two curved wave fronts are produces from the two "sources" (the slits).
 * The two wave fronts combine, they interfere constructively and destructively in different places.
 * An interference pattern is seen as bright and dark fringes.



The interference pattern is affected by the wavelength of the source, the length from the source to the screen (L) and the distance (d) between the slits. You can only use Young's formula when the angle (theta) is smaller than 10 degrees. When L and/or x is much, much bigger than d. The derivation of Young's is sometimes required for Excellence: Young's formula is: 

n here represents the nth nodal line <span style="color: #800080; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 120%;">(depending on which one you're interested in)

<span style="color: #800080; display: block; font-family: 'palatino linotype','book antiqua',palatino,serif; font-size: 120%; text-align: right;">Anti-nodal lines are whole numbers, nodal lines are "half numbers". <span style="color: #800080; display: block; font-family: 'palatino linotype','book antiqua',palatino,serif; font-size: 120%; text-align: left;">As you can see in the picture above (left), each line has it's own path and each has a different distance to travel. This is called the path difference.

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This video is awesome! I wish I was more like this fella!