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course Phy 202
7/13 11
Experiment 29: InterferenceUsing a hand-held laser pointer and a diffraction grating consisting of lines on a rectangular transparency, we observe the maxima created when the light is directed through the pattern at various separations, and with various incident angles. We determine the angular separation of the maxima and use this separation to estimate the wavelength of the light. We then use sets of parallel straight lines on the same transparency to determine the wavelength of the light.
Stapled to the paper rulers in your lab materials package is a rectangular transparency a few inches on a side. The transparency contains copies of various patterns of lines.
In at least one pattern the lines form a V.
• Orient the pattern so that the V is upright, with the widest spacing at the top.
• Move at least 3 and preferably 5 or more meters from a smooth wall. Shine the laser through the V near the top of the pattern and observe the image made by the light on the wall. Measure the distance from the transparency to the wall.
• Gradually move the laser down through the V, so that it shines between lines that move progressively closer and closer together. Observe what happens to the pattern on the wall.
• Continue moving down the V until you obtain the most distinct possible set of bright spots on the wall.
• Note the vertical position of the beam on the V.
• As best you can, determine for this position the average distance between the distinct bright spots formed on the wall.
• Measure the width of the V at this point, and the number of spaces between the threads across the width.
• Record also the distance to the wall.
There are also a few rectangular patterns consisting of parallel lines. The spacing of the lines varies from rectangle to rectangle.
• Repeat the preceding exercise using different rectangular grids.
• For each grid determine the average distance between the bright spots on the wall, the average distance between the grid lines and the distance from the plastic rectangle to the wall.
According to your results, how is the spacing between the bright spots on the wall related to the distance between the lines?
&&&&As the distance between the bright spots on the wall decreases, the distance between the lines increases.&&&&
What is the ratio of the spacing between the dots to the distance between the plastic rectangle and the wall?
&&&&From the wall to the rectangle, the distance was 140 inches and the distance between the dots was about 0.20 inches. The ratio is therefore 0.00143.&&&&
What distance is in the same ratio with the spacing between the lines?
&&&&0.00143&&&&
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You haven't mentioned the spacing between the lines on the grid.
The question is, what distance is in a .0014 ratio with the spacing of those lines.
&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes. &#
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