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

2.  Switch on the Sodium (Na) lamp. It takes about 20 minutes for it to warm up, and you will use it towards the end of the exercise.

3.  Set up the apparatus as shown in Figure 14-3. Use the Diffraction Plate and make sure that the filament of the Light Source is visible through the slot in the Diffraction Scale. View the light pattern through the double slit patterns of the Diffraction Plate (patterns D, E, and F). The slit spacing of these patterns is 0.125 mm, 0.250 mm, and 0.250 mm, respectively. Note that the slit spacing of E and F is the same. E and F are both double slits but F has slits that are twice as wide as E. Answer Question 1 on the Worksheet. You should see a combination of 2-slit interference fringes superimposed on a single slit diffraction pattern.

4.  Count the number of bright interference fringes that appear inside the central diffraction peak for slit D, E and F. Record the counts in cells C19:E19.

5.  Replace the Diffraction Plate with the Diffraction Grating. Remove the Slit Mask. View the first order spectrum through the grating. Carefully read the positions on the Diffraction Scale of the centers of the red, green, and blue sections of the spectrum. There is a first order spectrum on either side of the central maximum. Record the center positions for both first order spectra in cells C23:D25. Find the average values of s in each case and record in cells E23:E25. Record the distance D from the grating to the Diffraction Scale in cell D27. It may be helpful to attach the red, green and blue filters to the light source when viewing these spectral ranges.

6.  Record the readings for the right- and left-hand limits of the violet section and for the red section of the first order spectrum (both sides). Enter the results in cells C33:D36. Find the average values of s in each case and record in cells E33:E36.

7.  Look farther to each side and count how many "orders" you can see in the spectrum. This number may be color dependent - that is, you may be able to see more violet orders than red orders, for example. Record the result in cells D39:D41.

8.  Remove the white light source and replace it with the sodium source. Do not change the position of the grating or of the Diffraction Scale. It may be convenient to place the optical bench on top of the cardboard box so that the entrance slit is level with the opening in the lamp housing.