Young’s Double Slit Experiment

Sir Thomas Young achieved both conditions above by illuminating a double-slit aperture by filtered light which first passed through a tiny hole. He observed bright and dark interference fringes on a screen a distance L away with positions given by:

Bright fringes:	d sin(q) = ml,	y_bright = mlL/d
Dark fringes:	d sin(q) = (m + ½)l,	y_dark = (m + ½)lL/d

where l is the wavelength, d is the slit spacing, and m = 1, 2, ... is the order number.

The importance of Young’s experiment was that it unambiguously demonstrated the wave nature of light.