|
Interference and Diffraction
The lasers you will be working with today are very low power.
However, damage to your eye could occur if you look directly into the beam. If
there are two groups at your table, be sure that you have your lasers point away from one
another. The wavelength of the laser beam is 632.8 nm.
Set-up your laser on a lab jack at the end of the optical bench.
Use the lens holder to hold your multiple slit slide. Place the slits on the
end of the optical bench near the laser. The exact distance between the slits and
the laser doesn't matter. Place your screen 1 meter from the slits. Adjust the
laser beam so that it passes through the slits by raising or lowering the lab jack.
Part I: Single Slit
Observe and describe in your notebook the pattern of a laser beam
passing through a single slit.
Measure the locations of at least 6 minima. The easiest way
to do this is to hold scrap paper against the screen and make a very narrow mark at the
location of each minimum. Then move the paper to the tabletop and use your ruler to
measure the distance of each mark from the center. (Estimate to the nearest .5mm)
Make a quantitative sketch of intensity. Use graph paper.
The positions of the minimums should be accurate, but the intensity scale is only
relative.
Calculate the slit width for each your data points. Find the
average slit width and its percent uncertainty.
Part II: Two slits
Observe and describe in your notebook the interference patterns for
two slits.
Measure the locations of at least 6 interference minimums.
Make a quantitative intensity graph.
Calculate the slit spacing for each data point. Find the
average slit spacing and percent uncertainty.
Part III: More than 2 slits
Observe the patterns for 3, 4, 5, and 6 slits.
How are the patterns similar to the two-slit pattern? How are
they different?
Replace the slits with a diffraction grating. Change the slit
to screen distance to 10cm.
Measure the position of several diffraction maximums.
Calculate the slit spacing with percent uncertainty.
Determine the number of lines per centimeter in the grating.
Compare your calculation to the number supplied by the manufacturer.
|