PASCO Specialty & Mfg. SP-9268A User's Manual
Contents
1. Instruction Manual ies DU and Experiment Guide for the PASCO scientific Model SP 9268A STUDENT SPECTROMETER Copyright O January 1991 J O O l 10101 Foothills Blvd PO Box 619011 Roseville CA 95678 9011 USA m scientific Phone 916 786 3800 FAX 916 786 8905 email techsupp 9 PASCO com 012 02135F Spectrometer Table of Contents Section Page Equipment RSU A A ii Introduction DI a E T E 1 O 2 Eu 3 Meas rne Angl s O III ae ee 4 Using the Ditfrae on Grating aa 5 Using the Prism ana da 6 Maintenance sinsa un A 8 Appendix Using the Gaussian Eyepiece zu a 9 Technical SuDDODU nn u back cover Spectrometer 012 02135F Copyright Warranty and Equipment Return Please Feel free to duplicate this manual subject to the copyright restrictions below Copyright Notice The PASCO scientific Model SP 9268A Student Spec trometer manual is copyrighted and all rights reserved However permission is granted to non profit educational institutions for reproduction of any part of this manual providing the reproductions are used only for their laboratories and are not sold for profit Reproduction under any other circumstances without the written consent of PASCO scientific is prohibited Limited Warranty PASCO scientific warrants this product to be free from defects in materials and workmanship for a period of one2. mount To check the orientation of the grating look through the grating at a light source and notice how the grating disperses the light into its various color components When placed in the grating mount the grating should spread the colors of the incident light horizontally so rotation of the telescope will allow you to see the different colored images of the slit PASC GS scientific Figure 8 Perform steps 6 9 with reference to Figure 8 6 Rotate the telescope to find a bright slit image Align the vertical cross hair with the fixed edge of the im age and carefully measure the angle of diffraction See the previous section Measuring Angles of Dif fraction The diffraction grating diffracts the incident light into identical spectra on either side of the line of the un diffracted beam Rotate the telescope back past the zero diffraction angle to find the corresponding slit image Measure the angle of diffraction for this im age If the grating is perfectly aligned the diffraction angles for corresponding slit images will be identical If not use the table rotation fine adjust knob to com pensate for the difference i e to align the grating perpendicular to the collimator beam so the two angles will be equal Student Spectrometer 012 02135F 9 Repeat steps 6 8 until the angles for the correspond Wavelengths are determined according to the formula ing slit images are the same to within o
3. a particular color a precise image of the collimator slit can be seen For example when the telescope is at one angle of rotation the viewer might see a red image of the slit at another angle a green im age and so on By rotating the telescope the slit images corresponding to each constituent color can be viewed and the angle of diffraction for each image can be mea sured If the characteristics of the diffracting element are known these measured angles can be used to determine the wavelengths that are present in the light COLLIMATOR SLIT COLLIMATOR t LIGHT SOURCE PARALLEL BEAM P MN EYE PIECE 7 TELESCOPE ANGLE OF DIFFRACTION GREEN LIGHT DIFFRACTION GRATING OR PRISM Figure 1 Spectrometer Diagram e 1 Student Spectrometer 012 02135F The PASCO scientific Model SP 9268A Student Spec trometer provides precise spectroscopic measurements using either a prism or a diffraction grating as the dif fracting element The spectrometer includes the follow ing equipment see Fig 2 Collimator and Telescope Both the collimator and the telescope have 178 mm fo cal length achromatic objectives and clear apertures with 32 mm diameters The telescope has a 15X Ramsden eyepiece with a glass cross hair graticule The collimator is fitted with a 6 mm long slit of adjustable width Both the collimator and the telescope can be lev eled They can also b
4. see them IMPORTANT The grating is sandwiched be tween two glass slides so depending on how par allel the slides are you may see as many as four reflected images of the cross hairs In the follow ing steps you will be instructed to superimpose the graticule with its reflected image If there is more than one image just center the cross hairs as accurately as possible between the images 7 Use the table rotation fine adjust knob to align the vertical cross hair with its reflected image 8 Adjust the spectrometer table leveling screws until the cross hairs are superimposed on the reflected im age 9 Rotate the spectrometer table 180 and using the table rotation fine adjust knob align the vertical cross hair with the reflected image 10 Adjust the table leveling screws to remove half the separation between the horizontal cross hair and the reflected image Adjust the telescope leveling screws to remove the remaining error so the cross hairs and their reflected images are superimposed 11 Repeat steps 9 and 10 until the cross hairs and their reflected images are superimposed from both sides of the diffraction grating 12 Unplug the Gaussian eyepiece Adjust the slit of the collimator so it is open and vertical Student Spectrometer 012 02135F 13 Illuminate the slit with an external light source Ro tate the telescope directly opposite the collimator and focus the collimator only do not dis
5. Re tighten the lock ring and then refocus if necessary Realigning the Spectrometer 2 Focus the telescope at infinity This is best accom Under normal circumstances the spectrometer will main plished by focusing on a distant object e g out the tain its alignment indefinitely However if the spectrom nam eter can not be properly focused as described above it 3 Check that the collimator slit is partially open use may be necessary to adjust the optical axes of the colli the slit width adjust screw mator and telescope as follows 4 Align the telescope directly opposite the collimator 1 The telescope and collimator pivot about a fulcrum as shown in Figure 3 on their respective mounting pillars See Fig 4 Use the aluminum rod provided with the accessory equip ment to adjust the leveling screws Loosen one as the other is tightened until the unit is level and secure TELESCOPE COLLIMATOR ee e Edo LEVELING SCREWS MOUNTING PILLAR Figure 3 Align the Telescope directly opposite the Collimator Figure 4 Leveling the Telescope and Collimator Student Spectrometer 012 02135F 2 The mounting pillars of the telescope and collimator can be rotated by using an Allen wrench to loosen the screws that attach the pillars to their respective bases To loosen the screw for the collimator the spec trometer must be removed from the wood base 3 To be sure both optical u
6. ade with the prism aligned precisely as it was when the Pen graph was produced To ensure that this alignment can be reproduced all measurements are made with the prism aligned so that the light is refracted at the angle of minimum deviation DEFLECTED ANGLE A RAY Figure 9 Angle of Deviation E PASC CE scientific 012 02135F Student Spectrometer To Measure the Angle of Minimum Deviation 1 Align and focus the spectrometer as described earlier 2 Use the two thumbscrews to attach the prism clamp to the spectrometer table and clamp the prism in place as shown in Figure 10 3 Place the light source a few centimeters behind the slit of the collimator It may be helpful to partially darken the room but when using the prism this is of ten not necessary LIGHT SOURCE PRISM Figure 10 Mounting the Prism 4 With the prism it is generally possible to see the re fracted light with the naked eye Locate the general direction to which the light is refracted then align the telescope and spectrometer table base so the slit im age can be viewed through the telescope While looking through the telescope rotate the spec trometer table slightly back and forth Notice that the angle of refraction for the spectral line under observa tion changes Rotate the spectrometer table until this angle is a minimum then rotate the telescope to align the vertical cross hair with the fixe
7. ake certain there is at least two inches of packing material between any point on the apparatus and the inside walls of the carton 3 Make certain that the packing material can not shift in the box or become compressed thus letting the instrument come in contact with the edge of the box Address PASCO scientific 10101 Foothills Blvd P O Box 619011 Roseville CA 95678 9011 Phone 916 786 3800 FAX 916 786 8905 012 02135F Student Spectrometer Introduction In principle a spectrometer is the simplest of scientific instruments Bend a beam of light with a prism or dif fraction grating If the beam is composed of more than one color of light a spectrum is formed since the vari ous colors are refracted or diffracted to different angles Carefully measure the angle to which each color of light is bent The result is a spectral fingerprint which car ries a wealth of information about the substance from which the light emanates In most cases substances must be hot if they are to emit light But a spectrometer can also be used to investigate cold substances Pass white light which contains all the colors of the visible spectrum through a cool gas The result is an absorption spectrum All the colors of the vis ible spectrum are seen except for certain colors that are absorbed by the gas The importance of the spectrometer as a scientific instru ment is based on a simple but crucial fact Light
8. al cross hair 5 Place a light source preferably one with a discrete spectrum such as a mercury or sodium lamp ap proximately one centimeter from the slit Adjust the slit width so the slit image is bright and sharp If nec essary adjust the height of the spectrometer table so the slit image is centered in the field of view of the telescope IMPORTANT Stray light can obscure the im ages Use the spectrometer in a semi darkened room or drape a sheet of opaque material over the spectrometer TABLE ROTATION TABLE ROTATION FINE ADJUST KNOB 71 mii LIGHT SOURCE ANGLE OF DIFFRACTION ZERO Y DIFFRACTION VERTICAL CROSS HAIR SLIT IMAGE ANGLE OF DIFFRACTION VIEW THROUGH TELESCOPE SPECTROMETER TABLE LOCK SCREW LOCK SCREW SPECTROMETER TABLE BASE GRATING AND MOUNT gt m a 1cm M LIGHT lo SOURCE o o ssn cee Es VERNIER 2 nue d ats o o 8 Figure 7 Perform steps 2 5 with reference to Figure 7 2 Loosen the spectrometer table lock screw Align the engraved line on the spectrometer table so that it is as nearly as possible colinear with the optical axes of the telescope and the collimator Tighten the lock Screw Using the thumbscrews attach the grating mount so it is perpendicular to the engraved lines Insert the diffraction grating into the clips of the
9. cule with the fixed edge of the slit If the slit is For accurate results the diffracting element must be not vertical loosen the slit lock ring realign the slit properly aligned with the optical axes of the telescope and retighten the lock ring Adjust the slit width for a and collimator This requires that both the spectrometer clear bright image Measurements of the diffraction and the spectrometer table be level angle are always made with the graticule line aligned 1 Place the spectrometer on a flat surface If necessary along the fixed edge of the slit so a very narrow slit use paper or 3 X 5 cards to shim beneath the wood is not necessarily advantageous base until the fixed base of the spectrometer is level NOTE When the telescope and collimator are properly aligned and focused the slit should be sharply focused in the center of the field of view of 2 Level the spectrometer table by adjusting the three thumbscrews on the underside of the table Focusing the Spectrometer the telescope and one cross hair should be perpen dicular and aligned with the fixed edge of the slit 1 While looking through the telescope slide the eye If proper alignment cannot be achieved with the piece in and out until the cross hairs come into sharp adjustments just described you will need to re focus Loosen the graticule lock ring and rotate the align the spectrometer as follows graticule until one of the cross hairs is vertical
10. d edge of the slit image Use the fine adjust knobs to make these ad justments as precisely as possible then measure the telescope angle using the vernier scale Without changing the rotation of the spectrometer table remove the prism and rotate the telescope to align the cross hair with the fixed edge of the undiffracted beam Measure the angle on the vernier scale The difference between this angle and that re corded for the diffracted spectral line in step 5 is the angle of minimum deviation Notice that since the determination of the angle of minimum deviation for each spectral line requires rotational adjustments of the spectrometer table the angle of the undeflected beam must be remeasured for each line Student Spectrometer 012 02135F Maintenance Periodically clean the telescope aperture the collimator IMPORTANT Always handle the spectrometer P ea anil theprism wih a nonabtanive Tens pap s and its accessories with care to avoid scratching available at any camera store No other regular mainte the optical surfaces and throwing off the align nance is required ment Also when not in use the spectrometer should be stored in its hardwood case 012 02135F Student Spectrometer Appendix Using the Gaussian Eyepiece The optional Gaussian eyepiece Model SP 9285 sim plifies the task of aligning and focusing the spectrometer and aligning the diffraction grating O
11. e realigned though this is rarely necessary so that their optical axes are square to the axis of rotation Rotating Bases The telescope and the spectrometer table are mounted on independently rotating bases Vernier scales provide measurements of the relative positions of these bases to within one minute of arc The rotation of each base is controlled with a lock screw and fine adjust knob With the lock screw released the base is easily rotated by hand With the lock screw tight the fine adjust knob can be used for more precise positioning Diffraction grating and Mounting clamp Spectrometer table Slit plate Collimator Focus knob Slit width adjust screw Spectrometer table base Telescope base Table rotation Magnifying glass for reading Vernier Lock screw Fine adjust knob Spectrometer Table The spectrometer table is fixed to its rotating base with a thumbscrew so table height is adjustable Three level ing screws on the underside of the table are used to ad just the optical alignment The table must be level with respect to the optical axes of the collimator and tele scope if the diffracting element is to retain its alignment for all positions of the telescope Thumbscrews are used to attach the prism clamp and the grating mount to the table and reference lines are etched in the table for easy alignment Accessories Accessories for the spectrometer include a dense flint pris
12. h as a sodium or mercury vapor lamp If the alignment is correct corresponding spectral lines on opposite sides of the optical axis will have equal angles of diffraction If necessary adjust the rotation of the spectrometer table until the measurements are the same Technical Support FeedBack If you have any comments about this product or this manual please let us know If you have any suggestions on alternate experiments or find a problem in the manual please tell us PASCO appreciates any customer feed back Your input helps us evaluate and improve our product To Reach PASCO For Technical Support call us at 1 800 772 8700 toll free within the U S or 916 786 3800 email techsupp PASCO com Tech support fax 916 786 3292 WEB http www pasco com Contacting Technical Support Before you call the PASCO Technical Support staff it would be helpful to prepare the following information If your problem is computer software related note Title and Revision Date of software Type of Computer Make Model Speed Type of external Cables Peripherals f your problem is with the PASCO apparatus note Title and Model number usually listed on the label Approximate age of apparatus A detailed description of the problem sequence of events In case you can t call PASCO right away you won t lose valuable data If possible have the apparatus within reach when call ing This makes descripti
13. he light into a single spectrum whereas the grating divides the available light into several spec tra Because of this slit images formed using a prism are generally brighter than those formed using a grating Spectral lines that are too dim to be seen with a grating can often be seen using a prism lines is offset by a decreased resolution since the prism n2 doesn t separate the different lines as effectively as the su grating However the brighter lines allow a narrow slit 2 width to be used which partially compensates for the reduced resolution A D Unfortunately the increased brightness of the spectral sin 2 A where n is the index of refraction of the prism A is the angle between the sides of the prism traversed by the light With a prism the angle of refraction is not directly pro and D is the angle of minimum deviation Since n varies portional to the wavelength of the light Therefore to with wavelength the angle of minimum deviation also var measure wavelengths using a prism a graph of wave ies but it is constant for any particular wavelength length versus angle of refraction must be constructed us ing a light source with a known spectrum The wave length of unknown spectral lines can then be interpo lated from the graph UNDEELESTED LIGHT Once a calibration graph is created for the prism future II H iios wavelength determinations are valid only if they are ANGLE OF m
14. is emit ted or absorbed when an electron changes its orbit within an individual atom Because of this the spectrometer is a powerful tool for investigating the structure of atoms It s also a powerful tool for determining which atoms are present in a substance Chemists use it to determine the constituents of molecules and astronomers use it to de termine the constituents of stars that are millions of light years away In its simplest form a spectrometer is nothing more than a prism and a protractor However because of the need for very sensitive detection and precise measurement a real spectrometer is a bit more complicated As shown in Figure 1 a spectrometer consists of three basic compo nents a collimator a diffracting element and a tele scope The light to be analyzed enters the collimator through a narrow slit positioned at the focal point of the collimator lens The light leaving the collimator is therefore a thin parallel beam which ensures that all the light from the slit strikes the diffracting element at the same angle of incidence This is necessary if a sharp image is to be formed The diffracting element bends the beam of light If the beam is composed of many different colors each color is diffracted to a different angle The telescope can be rotated to collect the diffracted light at very precisely measured angles With the tele scope focused at infinity and positioned at an angle to collect the light of
15. m and two mounting clamps a 300 line mm diffrac tion grating and mounting clamp two thumbscrews for attaching the mounting clamps to the spectrometer table a magnifying glass for reading the vernier three Allen keys for leveling the telescope and collimator and a pol ished hardwood case NOTE A 600 line mm diffraction grating is avail able from PASCO as an optional accessory Optional Equipment Gaussian Eyepiece The Gaussian eyepiece SP 9285 is an optional compo nent that simplifies the task of focusing and aligning the spectrometer and aligning the diffraction grating Its use is described in the Appendix T Focus knob Eyepiece Graticule lock ring Telescope Telescope rotation Fine adjust knob Vernier scale Lock screw rem and Figure 2 eee Mounting clamp The Spectrometer I PASC Che scientific 012 02135F Student Spectrometer Equipment Setup 5 Looking through the telescope adjust the focus of the collimator and if necessary the rotation of the telescope until the slit comes into sharp focus Do not change the focus of the telescope NOTE If you are using the optional Gaussian Eyepiece SP 9285 equipment setup is somewhat simpler than described below See the Appendix for instructions 6 Tighten the telescope rotation lock screw then use Leveling the Spectrometer the fine adjust knob to align the vertical line of the grati
16. ne Gaussian eye piece can be used to align and focus any number of spec trometers so only one is generally needed per lab To Align and Focus the Spectrometer Using the Gaussian Eyepiece 1 Remove the telescope eyepiece and replace it with the Gaussian eyepiece 2 While looking through the telescope slide the eye piece in and out until the cross hairs come into sharp focus Loosen the graticule lock ring and rotate the graticule until one of the cross hairs is vertical Re tighten the lock ring and then refocus if necessary 3 Plug in the power supply of the Gaussian eyepiece The light from the eyepiece is reflected along the op tical axis of the telescope by a half silvered mirror Looking through the eyepiece you ll see the cross hairs lighted up as they scatter some of the light back into the eyepiece 4 Mount the grating holder to the spectrometer table and insert the diffraction grating 5 Looking through the telescope rotate the table until a patch of light is reflected back through the telescope from the glass surfaces of the grating The spec trometer table and the telescope must be at least roughly level to achieve this reflection If they are not see Realigning the Spectrometer earlier in the manual 6 Adjust the focus of the telescope until the cross hairs and their reflected images are in sharp focus The glass slides of the grating are not efficient reflectors so you must look carefully to
17. ne minute of fe ll ene arc Making the Reading where A is the wavelength a is the distance between oe ee as lines on the diffraction grating Once the grating is aligned do not rotate the rotating 3 A table or its base again Diffraction angles are measured a 3 3 d mm for the 300 line AE gra ng or as described in the previous section Measuring Angles 1 66 x 10 mm for the optional 600 line mm grating of Diffraction Since the vernier scales were moved 0 is the angle of diffraction and n is the order of the dif when the spectrometer table was adjusted the point of fraction spectrum under observation zero diffraction must be remeasured Using the Prism Advantages and Disadvantages The Angle of Minimum Deviation A prism can also be used as the diffracting element in a The angle of deviation for light traversing a prism is spectrometer since the index of refraction of the prism shown in Figure 9 For a given wavelength of light tra and therefore the angle of refraction of the light varies versing a given prism there is a characteristic angle of slightly depending on the wavelength of the light incidence for which the angle of deviation is a minimum This angle depends only on the index of refraction of the prism and the angle labeled A in Figure 8 between the two sides of the prism traversed by the light The rela tionship between these variables is given by the equa tion A prism refracts t
18. nits are square to the axis of rotation follow the focusing procedure described above adjusting the mounting pillars as necessary so the slit image is well centered in the viewing field of the telescope When analyzing a light source angles of diffraction are measured using the vernier scales However the scales only measure the relative rotational positions of the tele scope and the spectrometer table base Therefore before making a measurement it s important to establish a ver nier reading for the undeflected beam All angles of dif fraction are then made with respect to that initial reading see Fig 5 To obtain a vernier reading for the undeflected beam first align the vertical cross hair with the fixed edge of the slit image for the undeflected beam Then read the vernier scale This is the zero point reading 0 VERNIER READING FOR INDIEFRAGTED BEAM N ANGLE OF DIFFRACTION 0 0 i LET Mess SOURCE Qo vERNIER READING FOR UNDIFFRACTED EAM Figure 5 Measuring an Angle of Diffraction Now rotate the telescope to align the vertical cross hair with the fixed edge of a deflected image Read the ver nier scale again If this second reading is 0 then the ac tual angle of diffraction is 0 0 If the table base is ro tated for some reason the zero point changes and must be remeasured To read the angle first find where the zero point of the vernier scale alig
19. ns with the degree plate and record the value If the zero point is between two lines use the smaller value In Fig ure 6 below the zero point on the vernier scale is between the 155 and 155 30 marks on the degree plate so the recorded value is 155 Now use the magnifying glass to find the line on the ver nier scale that aligns most closely with any line on the degree scale In the figure this is the line corresponding to a measurement of 15 minutes of arc Add this value to the reading recorded above to get the correct measure ment to within 1 minute of arc that is 155 15 155 15 VER I 30 20 lO 170 160 15 on the vernier scale 155 on the degree scale 155 15 155 15 Figure 6 Reading the Vernier Scales PASCCH entific 012 02135F Student Spectrometer Using the Diffraction Grating IMPORTANT The Diffraction Grating is a deli cate component Be careful not to scratch the sur face and always replace it in the protective foam wrapping when it is not being used Aligning the Grating To accurately calculate wavelengths on the basis of dif fraction angles the grating must be perpendicular to the beam of light from the collimator 1 Align and focus the spectrometer as described earlier The telescope must be directly opposite the collima tor with the slit in sharp focus and aligned with the vertic
20. ons of individual parts much easier f your problem relates to the instruction manual note Part number and Revision listed by month and year on the front cover Have the manual at hand to discuss your questions
21. turb the telescope focus until the illuminated slit is in sharp focus If the collimator slit is not vertical loosen the lock ring align the slit vertically and then retighten the lock ring Then align the fixed edge of the slit with the vertical cross hair 14 Adjust the collimator leveling screws until the slit is vertically centered in the field of view of the tele scope As with the telescope you may need to ad just the collimator so that its optical axis is square to the axis of rotation The telescope collimator and spectrometer table are now properly aligned 15 If you are going to use the grating plug the Gaussian eyepiece back in and rotate the spectrometer table until the vertical cross hair is again aligned with its reflected image This insures that the grating is per pendicular to the optical axis of the spectrometer 16 If you wish you may replace the Gaussian eyepiece with the original eyepiece The focus of the tele scope will be maintained if you slide in the original eyepiece until the cross hairs are in sharp focus 10 Alignment Error The multiple reflections from the glass slides of the grat ing introduce some error into the alignment procedure Normally centering the cross hairs between the reflected images will reduce the error below the 1 minute resolu tion that is obtainable when reading the vernier scales To verify the alignment use a light source with discrete spectral lines suc
22. year from the date of shipment to the customer PASCO will repair or replace at its option any part of the product which is deemed to be defective in material or workmanship This warranty does not cover damage to the product caused by abuse or improper use Determi nation of whether a product failure is the result of a manufacturing defect or improper use by the customer shall be made solely by PASCO scientific Responsibil ity for the return of equipment for warranty repair belongs to the customer Equipment must be properly packed to prevent damage and shipped postage or freight prepaid Damage caused by improper packing of the equipment for return shipment will not be covered by the warranty Shipping costs for returning the equipment after repair will be paid by PASCO scientific Equipment Return Should this product have to be returned to PASCO scientific for whatever reason notify PASCO scientific by letter or phone BEFORE returning the product Upon notification the return authorization and shipping instructions will be promptly issued NOTE NO EQUIPMENT WILL BE ACCEPTED FOR RETURN WITHOUT AN AUTHORIZATION When returning equipment for repair the units must be packed properly Carriers will not accept responsibility for damage caused by improper packing To be certain the unit will not be damaged in shipment observe the following rules 1 The carton must be strong enough for the item shipped 2 M
Download Pdf Manuals
Related Search