Problem of the Week

Chapter 27: Quantum Theory

Problem of the Week

Wave Interference
Recall that when two or more waves interact, interference patterns are produced. Light sent through a diffraction grating produces a characteristic interference pattern. Even if just one photon at a time is sent through a grating, an interference pattern still forms. What would happen if a chunk of matter was sent though a grating? Does matter behave like a wave and produce interference patterns?

According to quantum theory, matter can exhibit wave properties.

Sodium Atom Interference?

<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078458137/193800/ch27_doubleSlit.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (3.0K)</a> David Pritchard of MIT sent a sodium atom through a grating with slits 100 nm wide. After two feet, the central beam and the first bright beam were 50 000 nm apart. These two beams are then made to intersect and the resulting interference patterns are studied. The suprising thing is that when only one atom of sodium is sent through Pritchard's apparatus, an interference pattern is still produced. Trying to visualize what happens as one atom passes through a grating and then have the appearance of two individual beams combining in an interference pattern will lead you into a quantum mechanical quagmire.

Based on the results of David Pritchard's apparatus, what is the wavelength of a sodium atom?

Estimate how long it takes a sodium atom to pass through Dr. Pritchards apparatus.

The apparatus is set up to show interference patterns for the wavelength you found in Problem One. Hypothetically speaking, suppose you wanted to send yourself through the apparatus, how long would it take before you observed your interference pattern?