1.  Open the Worksheet and fill in the header information.

I. Determination of the Laser Wavelength:

2.  See that the laser is firmly mounted at the 0 cm end of the optical bench as shown in Fig. 15-2.

3.  Clip a piece of paper to the foam board screen. Mount the screen and paper on the optical bench at the 125 cm mark.

4.  Mount the diffraction grating slide supplied (so that the rulings are vertical) to the slide holder and mount it on the optical bench close to the laser. Adjust the vertical and horizontal position of the slide so that the laser beam passes through the diffraction grating in the center of the slide.

5.  Turn on the laser, and mark the position of the zero order bright fringe on the paper (this would be the only bright spot on the screen with no grating in place). The position of the grating on the optical bench scale defines the distance D. Suppose the grating is at position x. The distance D is then equal to 125 cm - x. Enter the value in cell D9.

6.  On the paper, mark the positions of the first, second and third order bright fringes on each side of the zero order fringe.

7.  The grating slide will have the number of slits (or lines) per centimeter marked on it. Record this value in cell D12. The distance of separation between adjacent slits is the reciprocal of this value. Enter the computed value of d in cell D14.

♦♦♦ ALTERNATIVE ♦♦♦

7A.  If a traveling microscope is available, your instructor may have you measure d directly. Determine the distance between 25 lines on the grating and enter the value in cell F13. Divide this number by 25 and enter the result in cell D14.

II. Measuring the Width of a Hair:

8.  Tape a single strand of your hair over the hole in a 3 x 5 card and mount the card with the hair vertical to the optical bench at the 35 cm mark. Adjust the card position so that the hair intercepts the laser beam and produces a diffraction pattern on the screen.

9.  Raise or lower the screen so that this diffraction pattern does not overlap the pattern recorded earlier. On the paper mark the positions of at least the first 4 intensity minima on each side of the central bright spot (or however many you can observe). Also record the hair color.

10.  Repeat steps 8 and 9 with a strand of your partner's hair.

11.  Remove the paper from the clip on the Styrofoam. Measure and tabulate s on the right and on the left as observed with the grating, and enter these values in cells C19:D19. Calculate s_avg to be equal to one half the distance between the corresponding points on the left and right side, and enter the value in cell E19. Repeat for the second and third orders and record the values in cells C20:E21.