Diffraction and Interference
Objective: Determine the wavelength of the light emitted by the LASER.
Materials: diffraction grating, LASER, board, human hair, CD ROM
Caution:  LASER light is harmful to the retina of the eye.  DO NOT look directly into the laser aperture nor at reflections from metal or smooth surfaces.

Note:  rules for significant figures will be strictly enforced.  Use care with measurement unit s.

Methods and Analysis
1.  Set up and sketch the LASER bench as shown in class.  List all measurements to be taken.
2.  Locate and mount the slide containing the diffraction grating and record the distance (d) between slits.  Tape your data sheet to the screen and record the distance (L).
3.  Turn on the LASER and adjust the slide such that the LASER passes through the slits.  Adjust so the pattern is clear on the screen. Look for the closely spaced fringes.  Mark the locations of the centers of the bright fringes. Label the zeroth order and the symmetrically numbered orders out to the second order.  (2-1-0-1-2)
4.  Measure the distance (x) for the 0-1 and 1-2 adjacent orders on both sides of the zeroth order.  Determine the average of these four x values.  Retain at least 3 sig. figs.
5.  Apply Young's Interference Equation [λ = xd/L]  to determine the wavelength of the LASER light in meters and nanometers.
6. How does changing the d value affect x?  How does changing the L distance affect x?
7.  Tape a hair vertically across a slide and adjust the LASER to hit the hair.  Sketch the pattern on paper and record the location of the first bright spot on each side of center.  However, it may be more accurate to record the dark areas when determining the distance x.  Determine the thickness of the hair, d, using Young's equation.
8.  Record the necessary data for determining the spacing between ridges of the LASER reflecting off the CD ROM. [See Mr Keefer for the proper setup.]  Determine the spacing between the ridges on the CD ROM.

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