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course Phy 232
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 lines on the diffraction grating increases, the distance between the spots on the wall decrease. Therefore, the V with the more spacing between its lines results in less distance between spots on the wall.
What is the ratio of the spacing between the dots to the distance between the plastic rectangle and the wall?
The distance from the wall to the plastic rectangle is approximately 150 inches. The spacing between the dots was approximately .25 inches. Therefore the ratio between the dots to the distance between the plastic rectangle and the wall is .00167.
What distance is in the same ratio with the spacing between the lines?
The distance between the lines on the V on the diffraction grating to the distance from the plastic rectangle to the wall is in the same ratio as the spacing between the dots and the distance between the plastic rectangle and the wall.
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The last question asks you for for a specific distance.
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