Inventory Control
edited by JOE RICH Blackhawk Christian School Fall Wayne. IN
Multiport Student Spectrometer Carl 6. Bishop Clemson University, Clemson. SC 29634 Simple demonstrations that clearly portray physical evidence supporting the concept of quantized energy levels in the atomic theorv are difficult to find. Line soectra of the elements are the most obvious observation that is associated with quantized energy transitions of electrons. Several methods for observing line spectra using diffraction gratings and excited light sources have been described.'-3 In some of these methods, the spectra are observed without a reference scale, and therefore wavelenGhs cannot be calculated. Without quantitative data, t h e k t r u c t o r has a difficult task determining which lines have been observed by each student. This paper describes a relatively inexpensive spectrometer that can be used simultaneouslv " bv " seven students to observe a single spectrum emitted by an element or comoound in a sinele lieht tube aeainst a calibrated screen. The position of the observed lines can be sketched on a similar reproduced scale on a data sheet. T h e light tuhe sources can be quickly changed, and each student can observe and diagram the spectraof e i ~ hto t 10 sources in a 30-minute period. if two students share-each observation port, observing and sketching alternately, 14 students can perform the experiment in a sliehtlv .. .loneer time. Several educational equipment companies4~'sellspectrum tuhes for allout 18 different elements or comoounds. These companies also have high-frequency generators to excite the suhstances,and diffractioncratinas (13.400 linewin.) on film in 2-in. X 2-in. slide holders. ~ h ~ c & & gprice of the spectrum tubes will vary from $13 to $20 each, the high-frequency generator about $80 to $120, and the diffraction gratings about 25 gratings for $12. A list of the materials used t o construct the spectrometer is given below. Most dimensions are given in inches to correspond with commercially available wood products. Equivalent metric dimensions may be used.
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a. 148- X 63- X 3/&. plywood h. 8 2%- X 22- X %-in. wooden strips c. 18 2- X 12- X 3/4-in.wooden strips d. 12'14-in. thick wooden wedge e. 2 2- X 4- X %-in. metal plates f. 14 2%- X 1-X 3/&. wooden hlwks g. 185-cmmetal strip about '/2 in. wide h. cardboard pieces as a cover
i. 50 3p nails j. wood glue
k. 7 diffraction gratings 1. 7 clear plastic metric rulers m. 30 thumb tacks n. 7 2Y- X 3/r- X 14-in. wooden strips o. 8 small wood screws '12 in. long
Assembly of the Spectroscope (Refer to Flg. 1) Determining the Seven Light Paths 1. Locate the position of the light source center on the plywood sheet (a) by measuring 79 em in from the long side of the large
Figure 1. This is me layout of lhe spectmrnetershowing the positions of seven ports (dehactlon gratings),the light source, and me seven spectrum scales used to calculate me angle of deflection of each observed line. The stio~led .. porlions in the diagram are cut away fromthe plywaad sheet and can be used to make omer pans of the spedascope. plywood sheet and half way between the short sides. Drive a 3p nail at this point as a pivot point leaving 3 cm of the nail exposed. 2. Drill a %-in. pivot hole near one end of an 85-cm metal strip (g). (A portion of a metal band from a packing crate or from a pad of bricks may he used.) Carefully drill three more Y-in. holes 50 cm, 77 em, and 79 cm from the first pivot hole. (These holes will be refered to as the 50-cm, 77-cm, and 79-cm holes, respectively.) This strip will be used to draw arcs with specific radii.
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Reiss, E. J. Chem. Educ. 1988,65,517-518. 2Corlel,A,: Fernandez. L. J. Chem. Educ. 1986,63.348-349. Driscoll, J. A. J. Chem. Educ. 1974,51,97. Biology/Science Materials Catalog ( 1986-87): Carolina Biological Supply: Burlington. NC 27215; pp 1098-1099. Fisher-EMD Catalog ( 1988/89): Fisher Scientific: Educational Materials Division, 4901 W. LeMoyne Street, Chicago. IL 60651; p C130. Volume 66
Number 12 December 1989
1037
3. Place the pivot hole of the metal strip from Step 2 over the pivot nail on the plywood sheet (a). 4. Place a pencil point through the 79-cm hole in the metal strip, and draw an arc across the plywood sheet from edge to edge. Place the pencil point in the 77-cm hole, and draw a second are from edge to - - edes. ---5. Looking from the arc side toward the pivot nail on the plywood sheet, drivea3p pivot nailon the left side 2.5rm frum theedge ofrhe plywood on the 79-cm arc. Place the pivot hole uf the metal strip over this nail, and mark a point on the 79-cm arc using the 50-cm hole. Drive in another pivotnail at that point and repeatthis process five times. (There will he seven nails on the 79-an arc.) 6. Draw a straight line from the Light source center to each nail on the 79-cm Line (seven Lieht . .. oaths).. Remove all the nails on the 79-cm arc. L'sc a protrnetnr or a right angle todraw a line4 rm long on each side of and perpendicular to the light paths where each line rrossrs the 77-em arc. 7. Cut along the 79-cm arc with a saber saw or a hand saw. (These scrap pieces may be used later to cut some of the curved strips in Step 14.) ~~~~
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Locating the Light Source Tubes 8. Cut a 2%-in. thick wooden wedge (d) about 12 em long that will fit between the fourth and fifth light paths, and leave 0.4 em elearance oneach side for the light path. Cut off the sharp end about 4 cm from the light source point. 9. File a semicircular notch in the narrow end of each (2- X 5- X l/s-in.) metal plate (e) to fit around the narrow portion of aspectrum tuhe. At the opposite end, drill four holes in each plate for small wood screws (0). 10. Drive the light source center pivot nail straight through the plywood. Use wood screws to attach one notched metal plate on the bottom side of the plywood with the notch centered around the nail. (This will center the light source tube.) Outline the plate with a pencil, and then remove the screws and metal plate. 11. Place the second metal plate an top of the wwden wedge, and center the notch ahove the lieht source nail. Carefullv attach the plate with wood screws. Mark the position
