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Double slit diffraction

This applet shows what happens when plane waves travel through two narrow slits: from the slits two waves emerge in phase and propagates in the right side of the page. Acting on the sliders you can change the wavelength (lambda) of the waves or the angle toward which they travel. For wavelengths small compared to the distance between the slits there is no clear interference pattern, nor when lambda is much higher. If the wavelength is of the same order of magnitude of the slits distance, a characteristic diffraction figure appears. The green dot labeled "Total Amplitude" shows the sum of the two waves computed summing the amplitude of each wave at the place where green dots appear on them. Changing the angle toward which the waves propagate, you can see the amplitude changing. Try to follow the green dots on the waves and the "Total Amplitude", for different values of lambda.