| A laser shines
through a variable slit pattern forming an interference pattern
on a white screen two meters away. The slit pattern is mounted on
a slide which the visitor can move up and down changing from a single
slit to a double slit as well as changing the width of the single
slit or the spacing of the two slits. The single slit diffraction
pattern on the screen changes as the slit width changes. In fact
the width of the diffraction pattern is inversely proportional to
the size of the slit. The diffraction pattern of the double slit
also varies its size in inverse proportion to the slit spacing.
In addition, the diffraction pattern spreads out horizontally even
though the slit is a vertical slit. This spreading is a result of
the Heisenberg uncertainty principle.