ADVANCED LAB PHY 4822L
Popular in Course
Popular in Physics 2
This 26 page Class Notes was uploaded by Garett Kovacek on Thursday September 17, 2015. The Class Notes belongs to PHY 4822L at Florida State University taught by Staff in Fall. Since its upload, it has received 102 views. For similar materials see /class/205525/phy-4822l-florida-state-university in Physics 2 at Florida State University.
Reviews for ADVANCED LAB
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 09/17/15
Instruction Manual 01 and Experiment Guide for the PASCO scienti c Model AP9368 and AP9369 he Apparatus and he Apparatus Accessory Kit 1989 PASCO scientific 500 better A q 10101 Foothills Blvd Roseville CA 957477100 c I 9 II t I f I 9 Phone 9167866800FAX916786 8905wwmpascocom 01204049 he Apparatus and We Apparatus Accessory Kit Table of Contents Section Page Copyright Warranty and Equipment Return ii 1 J 1 Background Theory 2 Equipment and Setup 3 Equipment List 3 Installing the Batteries 3 Battery Voltage Check 3 Equipment Setup 4 Using the Accessory Kit Filters 6 Experiments Experiment 1 Wave Model vs Quantum Model 7 Experiment 2 The Relationship of Energy Wavelength and Frequency 11 Technical Information 13 Theory of Operation 13 quot Diagram 14 Teacher s Guide 15 Technical Support Inside Back Cover he Apparatus and he Apparatus Accessory Kit 01204049J Copyright Warranty and Equipment Return Please Feel free to duplicate this manual subject to the copyright restrictions below Copyright Notice The PASCO scientific 01204049 he Apparatus and he Apparatus Accessory Kit manual is copyrighted and all rights reserved However permission is granted to nonpro t educational institutions for reproduction of any part of the manual providing the reproductions are used only for their laboratories and are not sold for pro t Reproduction under any other circumstances without the written consent of PASCO scientific is prohibited Limited Warranty PASCO scientific warrants the product to be free from defects in materials and workmanship for a period of one 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 The warranty does not cover damage to the product caused by abuse or improper use Determination of whether a product failure is the result of a manufacturing defect or improper use by the customer shall be made solely by PASCO scienti c Responsibility 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 im proper 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 scienti c Credits This manual edited by Dave Griffith Teacher s guide written by Eric Ayar Equipment Return Should the product have to be returned to PASCO scienti c for any reason notify PASCO scienti c by letter phone or fax BEFORE returning the product Upon notification the return authorization and ship ping instructions will be promptly issued NOTE NO EQUIPMENT WILL BE ACCEPTED FOR RETURN WITHOUT AN AUTHORIZATION FROM PASCO 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 D The packing carton must be strong enough for the item shipped Make certain there are at least two inches of pack ing material between any point on the apparatus and the inside walls of the carton 3 Make certain that the packing material cannot shift in the box or become compressed allowing the instrument come in contact with the packing carton Address PASCO scienti c lOlOl Foothills Blvd Roseville CA 957477100 Phone 916 7863800 FAX 916 7863292 email techsupppascocom web wwwpascocom 174301 cnnnnn 01204049J he Apparatus and We Apparatus Accessory Kit Ii Introduction The emission and absorption of light was an early subject for investigation by German physicist Max Planck As Planck attempted to formulate a theory to explain the spectral distribution of emitted light based on a classical wave model he ran into considerable dii culty Classical theory RayleighJeans Law predicted that the amount of light emitted from a black body would increase dramati cally as the wavelength decreased whereas experiment showed that it approached zero This discrepancy became known as the ultraviolet catastrophe Experimental data for the radiation of light by a hot glowing body showed that the maximum intensity of emitted light also departed dramatically from the clas sically predicted values Wien s Law In order to rec oncile theory with laboratory results Planck was forced to develop a new model for light called the quantum model In this model light is emitted in small discrete bundles or quanta The relationship between the classical and quantum theo ries for the emission of light can be investigated using the PASCO scienti c he Apparatus Using the Apparatus in combination with the PAS CO Mercury Vapor Light Source Model 039286 allows an accurate determina tion of the he ratio and thus a determination of h Planck39s constant Figure 1 The he Apparatus Shown V th the Accessory Kit and Mercury Vapor Light Source he Apparatus and We Apparatus Accessory Kit 01204049J li Background Theory Planck39s Quantum Theory By the late 180039s many physicists thought they had ex plained all the main principles of the universe and discov ered all the natural laws But as scientists continued work ing inconsistencies that couldn39t easily be explained be gan showing up in some areas of study In 1901 Planck published his law of radiation In it he stated that an oscillator or any similar physical system has a discrete set of possible energy values or levels en ergies between these values never occur Planck went on to state that the emission and absorption of radiation is associated with transitions or jumps be tween two energy levels The energy lost or gained by the oscillator is emitted or absorbed as a quantum of radiant energy the magnitude of which is expressed by the equa tion Ehv where E equals the radiant energy v is the frequency of the radiation and h is a fundamental constant of nature The constant 11 became known as Planck39s constant Planck39s constant was found to have signi cance beyond relating the frequency and energy of light and became a comerstone of the quantum mechanical view of the suba tomic world In 1918 Planck was awarded a Nobel prize for introducing the quantum theory of light The Photoelectric Effect In photoelectric emission light strikes a material causing electrons to be emitted The classical wave model pre dicted that as the intensity of incident light was increased the amplitude and thus the energy of the wave would in crease This would then cause more energetic photoelec trons to be emitted The new quantum model however predicted that higher frequency light would produce higher energy photoelectrons independent of intensity while increased intensity would only increase the number of electrons emitted or photoelectric current In the early 1900s several investigators found that the kinetic energy of the photoelectrons was dependent on the wave length or frequency and independent of intensity while the magnitude of the photoelectric current or number of electrons was dependent on the intensity as predicted by the quantum model Einstein applied Planck39s theory and explained the photoelectric effect in terms of the quantum model using his famous equation for which he received the Nobel prize in 1921 Ehv KE W max 0 where KE is the maximum kinetic energy of the emit ted photoelzexctrons and W0 is the energy needed to re move them from the surface of the material the work function E is the energy supplied by the quantum of light known as a photon The he Experiment A light photon with energy hv is incident upon an elec tron in the cathode of a vacuum tube The electron uses a minimum W0 of its energy to escape the cathode leaving it with a maximum energy of KEW in the form of kinetic energy Normally the emitted electrons reach the anode of the tube and can be measured as a photoelectric current However by applying a reverse potential Vbetween the anode and the cathode the photoelectric current can be stopped KEWU can be determined by measuring the mini mum reverse potential needed to stop the photoelectrons and reduce the photoelectric current to zero Relating kinetic energy to stopping potential gives the equation KEWU Ve Therefore using Einstein39s equation 11 v V8 W0 When solved for V the equation becomes V 1112 v WCe If we plot Vvs v for different frequencies of light the graph will look like Figure 2 The Vintercept is equal to WOe and the slope is 118 Coupling our experimental de termination of the ratio 118 with the accepted value for 8 1602 x 103919 coulombs we can determine Planck39s constant 11 Stopping Potential V Frequency v Figure 2 The graph of V vs v NOTE In experiments with the PASCO he Ap paratus the stopping potential is measured directly rather than by monitoring the photoelectric current See the Theory of Operation in the Technical Infor mation section of the manual for details MENU c 01204049J he Apparatus and We Apparatus Accessory Kit ll Equipment and Setup Filters hle Apparatus AP9368 Mercury Vapor light Source 089286 LensG rating Light Aperture Assembly Assembly Support Base Assembly Light Block for a Light Source I hle Apparatus Accessory Kit AP9369 Coupling Bar Assembly Figure 3 hle Equipment Identification These items may be purchased separately from PASCO scienti c or together as an AP9370 he System 174301 SDIlntlIc Equipment Required iDigital voltmeter SE9589 7 he Apparatus AP9368 7 he Apparatus Accessory Kit AP9369 iMercury Vapor Light Source OS 9286 Installing the Batteries The he Apparatus requires two 9volt batteries supplied but not installed The battery compartment is accessed by loosening the thumbscrew on the rear end panel and re moving the cover plate gt NOTE The he Apparatus can also be powered using a i9 V dual power supply Just remove the batteries and connect 9 V to the quot6 V MINquot bat tery test terminal and 9 V to the quot6 V lVIIN bat tery test terminal Battery Voltage Check Although the he Apparatus draws only a small amount of current and batteries normally last a long time it39s a good idea to check the output voltage before each use Battery test points are located on the side panel of the Apparatus near the ONOFF switch Batteries functioning below the recommended minimum operating level of 6 volts may cause erroneous results in your experiments To check the batteries use a voltmeter to measure be tween the OUTPUT ground terminal and each BATTERY TEST terminal 6V MIN and 6V MIN If either battery tests below its minimum rating it should be replaced before running experiments Battery Test Terminals j ONOFF Switch Ground Terminal Figure 4 Battery Test Points he Apparatus and We Apparatus Accessory Kit 01204049J THE CONTROLS 1 Press to discharge the instrument he Apparatus ONOFF Switch Connect to a digital voltmeter the output is a direct measurement of the stopping potential Support Base Assembly Light Aperture Assembly Light Source LensGrating Assembly Coupling Bar Assembly Figure 5 Equipment Setup Using a Mercury Vapor Light Source and the We Apparatus Equipment Setup The standard setup for he experiments is shown in Figure 5 Details for setting up the apparatus are described below 1 N U The Light Source design allows simultaneous connec tion of two Light Aperture assemblies one on the front and one on the back If you are using only one Light Aperture and he Apparatus install the Light Block supplied with the Accessory Kit in the mount ing groove closest to the body of the housing on the back of the Light Source see Figure 6 Slide the Light Aperture Assembly into the center mounting groove on the front of the Light Source Secure it in place by fingertightening the two thumb screws against the front of the Light Source housing The LensGrating Assembly mounts on the support bars of the Light Aperture Assembly Figure 7 Loosen the thumbscrew slip it over the bars and fingertighten the thumbscrew to hold it securely Light Block I Rear Channel f Mercu Light Source Figure 6 Installing the Light Block gt NOTE The grating is blazed to produce the brightest spectrum on one side only During your experiment you may need to turn the LensGrating Assembly around in order to have the brightest spectrum on a convenient side of your lab table 8 Figure 7 LensGrating Mounting Detail 1743 l cllnPIID 01204049J he Apparatus and We Apparatus Accessory Kit e Turn on the Light Source and allow it to warm up for ve minutes Check the alignment of the Light Source and the Aperture by looking at the light shining on the back of the LensGrating assembly If necessary adjust the back plate of the Light Aperture Assembly by loos ening the two retaining screws Figure 8 and sliding the aperture plate left or right until the light shines di rectly on the center of the LensGrating Assembly Figure 8 Light Aperture Adjustment V39 Insert the Coupling Bar assembly into the lower mounting groove of the Light Source Figure 5 Se cure in place by tightening the thumbscrew against the front of the Light Source housing 0 Remove the screw from the end of the Support Base rod Insert the screw through the hole in the Support Base plate and attach the rod to the Support Base plate by tightening the screw use Phillips drive screwdriver gt1 Place the he Apparatus onto the Support Base Assembly 00 Place the Support Base assembly over the pin on the end of the Coupling Bar assembly Connect a digital voltmeter DVM to the OUTPUT terminals of the he Apparatus Select the 2V or 20V range on the meter 10 Set the he Apparatus directly in front of the Mercury Vapor Light Source By sliding the LensGrating as sembly back and forth on its support rods focus the light onto the white re ective mask of the he Appara tus Figure 9 0 Window to White Photodiode Mask White Reflective Mask Light Shield shown tilted to Base Support Rod he open position Figure 9 hle Light Shield 11 Roll the light shield of the Apparatus out of the way to reveal the white photodiode mask inside the Appara tus Rotate the he Apparatus until the image of the aperture is centered on the window in the photodiode mask Then tighten the thumbscrew on the base support rod to hold the Apparatus in place 12 As in step 9 slide the LensGrating assembly back and forth on its support rods until you achieve the sharpest possible image of the aperture on the window in the photodiode mask Tighten the thumbscrew on the Lens Grating assembly and replace the light shield Turn the power switch ON Rotate the he Apparatus about the pin of the Coupling Bar Assembly until one of the colored maxima in the first order shines directly on the slot in the white re ective mask Rotate the he Apparatus on its support base so that the same spectral maxima that falls on the opening in the White Re ec tive Mask also falls on the window in the photodi ode mask LA gt NOTE The white re ective mask on the he apparatus is made of a special uorescent material This allows you to see the ultraviolet line as a blue line and it also makes the violet line appear more blue You can see the actual colors of the light if you hold a piece of white non uorescent material in front of the mask The palm of your hand works in a pinch although it uoresces enough that the UV line will still be visible When making measurements it is important that only one color falls on the photodiode window There must be no overlap from adjacent spectral m axim a he Apparatus and We Apparatus Accessory Kit 01204049J White I O 03 Z Ultraviolet 0 ViiLiJ Green Yellow 2nd and 3rd Order Overlap Green amp Yellow Spectral lines in 3rd Order are not Visible Color Frequency Hz Wavelength nm All values except wavelength for yellow line are from Handbook of Chemistry and Physics 46th ed Yellow 539 18672E14 578 The wavelength of the yellow was determined ex Green 548996E14 546074 Perimentally using a 6001iIIemm grating Blue 687858E14 435835 NOTE The yellow line is actually a doublet Violet 740858E14 404656 Wlth wavelengths Of 578 and 580mm Ultraviolet 820264E14 365483 Figure 10 The Three Orders of Light Gradients 14 Press the PUSH TO ZERO button on the side panel Using the Filters Of ie We Appaiatus to discharge f I y f ccumulated P0 The AP9368 he Apparatus includes three lters one tentlal m the umt s elecnomcs39 Thls W111 assure the AP Green and one Yellow plus a Variable Transmission Filter Params records only the Pmentlal Of le hght you are The lter frames have magnetic strips and mount to the out measuring Note thatthe outputvoltage will driftwith d fth WhiteR ti Mask fth 11 ms the absence of light on the photodiode SI 6 0 e e 60 V6 0 e e Appara 39 Use the green and yellow lters when you re using the green and yellow spectral lines These lters limit higher frequencies of light from entering the he Apparatus This prevents ambient room light from interfering with the lower energy yellow and green light and masking the true results It also blocks the higher frequency ultraviolet light from the higher order spectra which may overlap with lower orders of yellow and green 15 Read the output voltage on your digital voltmeter It is a direct measurement of the stopping potential for the photoelectrons See Theory of Operation in the Tech nical Information section of the manual for an expla nation of the measurement gt NOTE For some apparatus the stopping poten tial will temporarily read high and then drop down to the actual Stopping Potential voltage The Variable Transmission Filter consists of computer generated patterns of dots and lines that vary the intensity not the frequency of the incident light The relative trans mission percentages are 100 80 60 40 and 20 6 MENU c 01204049J he Apparatus and We Apparatus Accessory Kit Experiment 1 The Wave Model of light vs the Quantum Model According to the photon theory of light the maximum kinetic energy KEW of photoelectrons depends only on the frequency of the incident light and is independent of the intensity Thus the higher the frequency of the light the greater its energy In contrast the classical wave model of light predicted that Kme would depend on light inten sity In other words the brighter the light the greater its energy This lab investigates both of these assertions Part A selects two spectral lines from a mercury light source and investigates the maximum energy of the photoelectrons as a function of the intensity Part B selects different spectral lines and investigates the maximum energy of the photoelectrons as a function of the frequency of the light Setup Set up the equipment as shown in the diagram below Focus the light from the Mercury Vapor Light Source onto the slot in the white re ective mask on the he Apparatus Tilt the Light Shield of the Apparatus out of the way to reveal the white photodiode mask inside the Appara tus Slide the LensGrating assembly forward and back on its support rods until you achieve the sharpest image of the aperture centered on the hole in the photodiode mask Secure the LensGrating by tightening the thumbscrew Align the system by rotating the he Apparatus on its support base so that the same color light that falls on the opening of the light screen falls on the window in the photodiode mask with no overlap of color from other spectral lines Return the Light Shield to its closed position Check the polarity of the leads from your digital voltmeter DVM and connect them to the OUTPUT terminals of the same polarity on the he Apparatus Experiment 1 Equipment Setup he Apparatus and We Apparatus Accessory Kit 01204049J Procedure Pa rt A 1 Adjust the he Apparatus so that only one of the spectral colors falls upon the opening of the mask of the photodiode If you select the green or yellow spectral line place the corresponding colored lter over the White Re ective Mask on the he Apparatus Place the Variable Transmission Filter in front of the White Re ective Mask and over the colored lter if one is used so that the light passes through the section marked 100 and reaches the pho todiode Record the DVlVI voltage reading in the table below N Press the instrument discharge button release it and observe approximately how much time is re quired to return to the recorded voltage E Move the Variable Transmission Filter so that the next section is directly in front of the incoming light Record the new DVM reading and approximate time to recharge a er the discharge button has been pressed and released Repeat Step 3 until you have tested all ve sections of the lter Repeat the procedure using a second color from the spectrum Color 1 Transmission Stopping Potential Approx Charge name Time 100 Color 2 Transmission Stopping Potential Approx Charge name Time 100 01204049J he Apparatus and We Apparatus Accessory Kit Part B 1 SAN You can easily see ve colors in the mercury light spectrum Adjust the he Apparatus so that only one of the yellow colored bands falls upon the opening of the mask of the photodiode Place the yellow colored lter over the White Re ective Mask on the he Apparatus Record the DVMvoltage reading stopping potential in the table below Repeat the process for each color in the spectrum Be sure to use the green lter when measur ing the green spectrum Analysis 1 N E Describe the effect that passing different amounts of the same colored light through the Vari able Transmission Filter has on the stopping potential and thus the maximum energy of the photoelectrons as well as the charging time after pressing the discharge button Describe the effect that different colors of light had on the stopping potential and thus the maximum energy of the photoelectrons Defend whether this experiment supports a wave or a quantum model of light based on your lab results Explain why there is a slight drop in the measured stopping potential as the light intensity is decreased gt NOTE While the impedance of the zero gain ampli er is very high 41013 9 it is not infmite and some charge leaks off Thus charging the apparatus is analogous to lling a bath tub with different water ow rates while the drain is partly open Light Color Stopping Potential Yellow Green Blue Violet Ultraviolet he Apparatus and We Apparatus Accessory Kit 01204049J Notes 01204049J he Apparatus and We Apparatus Accessory Kit Experiment 2 The Relationship between Energy Wavelength and Frequency According to the quantum model of light the energy of light is directly proportional to its frequency Thus the higher the frequency the more energy it has With careful experimentation the constant of proportionality Planck39s constant can be determined In this lab you will select different spectral lines from mercury and investigate the maximum en ergy of the photoelectrons as a function of the wavelength and frequency of the light Setup Set up the equipment as shown in the diagram below Focus the light from the Mercury Vapor Light Source onto the slot in the white re ective mask on the he Apparatus Tilt the Light Shield of the Apparatus out of the way to reveal the white photodiode mask inside the Apparatus Slide the LensGrating assembly forward and back on its support rods until you achieve the sharpest im age of the aperture centered on the hole in the photodiode mask Secure the LensGrating by tight ening the thumbscrew Align the system by rotating the he Apparatus on its support base so that the same color light that falls on the opening of the light screen falls on the window in the photodiode mask with no overlap of color from other spectral bands Return the Light Shield to its closed position Check the polarity of the leads from your digital voltmeter DVM and connect them to the OUT PUT terminals of the same polarity on the he Apparatus Experiment 2 Equipment Setup he Apparatus and We Apparatus Accessory Kit 01204049J Procedure 1 N 3 You can see ve colors in two orders of the mercury light spectrum Adjust the he Apparatus carefully so that only one color from the first order the brightest order falls on the opening of the mask of the photodiode For each color in the first order measure the stopping potential with the DVM and record that measurement in the table below Use the yellow and green colored lters on the Re ective Mask of the he Apparatus when you measure the yellow and green spectral lines Move to the second order and repeat the process Record your results in the table below Analysis Determine the wavelength and frequency of each spectral line Plot a graph of the stopping potential vs frequency Determine the slope and yintercept Interpret the results in terms of the 118 ratio and the WUe ratio Calculate h and W0 In your discussion report your values and discuss your results with an interpretation based on a quantum model for light First Order Wavelength Frequency Stopping Potential Color nm x1014 Hz volts Yellow Green Blue Violet Ultraviolet Second Order Wavelength Frequency Stopping Potential Color nm x10 Hz volts Yellow Green Blue Violet Ultraviolet 01204049J he Apparatus and We Apparatus Accessory Kit ll Technical Information Theory of Operation In experiments with the he Apparatus monochromatic light falls on the cathode plate of a vacuum photodiode tube that has a low work function W0 Photoelectrons ejected from the cathode collect on the anode The photodiode tube and its associated electronics have a small capacitance which becomes charged by the photo electric current When the potential on this capacitance reaches the stopping potential of the photoelectrons the current decreases to zero and the anodetocathode volt age stabilizes This final voltage between the anode and cathode is therefore the stopping potential of the photoelectrons To let you measure the stopping potential the anode is connected to a builtin ampli er with an ultrahigh input impedance gt 1013 Q and the output from this ampli er is connected to the output jacks on the front panel of the apparatus This high impedance unity gain V outV in l ampli er lets you measure the stopping potential with a digi tal voltmeter Due to the ultra high input impedance once the capacitor has been charged from the photodiode current it takes a long time to discharge this potential through some leak age Therefore a shorting switch labeled PUSH TO Zero enables the user to quickly bleed off the charge However the opamp output will not stay at 0 volts a er the switch is released since the opamp input is oating Due to variances in the assembly process each appara tus has a slightly different capacitance When the zero switch is released the internal capacitance along with the user39s body capacitance coupled through the switch is enough to make the output volatge jump andor os cillate Once photoelectrons charge the anode the input voltage will stabilize 01204049J he Apparatus and We Apparatus Accessory Kit I 49733 8 R1 1K OUTPUT PD1 VACUUM PHOTODIODE 1P39 PUSH TO 32 ZERO J3 4 P34 P3 5J35 I 39 J3 4 P1 4 BATTERY TEST 39 II 39 VW P31 gtgtJ31 6V MIN J3 4 P1 4 1R 9V A J15 P15 P21J21 A o J2 4 P2 4 BAT1 T 9v T 31 A ONOFF 139 BAT2 J2 5 P2 5 T J11 EP11 u P223 J2 2c gFF ON P3 2 J3 2 W gtgt 393 6V MIN R3 1K Schematic Diagram muoqu We Appavams and We Appamus Aeeessw m Teacher s Guide Part In aseLh W I I me to reach full oltagemcreases s A many 5 uh deeeeasmg Z intensity u g ammutefor E 20 mtensxty as o o o o a v v v v ns M M m 2n an 10 su an w an snx PerB Mann6 Analysis 5 Sigm candy affect me 3 msmmsx o 4 muzs ou stoppingpotennal 1mm msmeunmemee a affecttheum xttakesto a mhms pot a1 From ix422255uE715x Haasza ou t ecmdetmmethm R 29942518E39lsecammder themtensxty ome kg 1 aff thenumberofel tronsemmedbutnt e maximum energy ofthe M electrons n2 2 maximumeney a a a a a a ofthephotoelectronsThe g g g g g g g g relauonshxpappearstobe 39 N quot gmmmz w F m unear 3 Thxs expenmentsuppons a quantum model oflxght zeror w mm 7 armmg and the electrons leavmg through the amplifier becomes lower MixE 1s me Appavmusand m2 APPBVB usAnuesmwm mzmmw Exp e Apparatus and Accessary Klf Analysis 5 3 145193519X 1412u29Eou 94252424 Rm alder a Firslnn ler 5 a g M 2225mmx 4 455mm a 2 425mm 52mm mu F g g u g a an n4 n2 Q Q Q Q Q Q Q Q 7 N m Fvequemv z In F m 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 cus tomer feedback Your input helps us evaluate and improve our product To Reach PASCO For Technical Support call us at 18007728700 tollfree within the US or 916 7863 800 ax 916 7863292 e mail techsupppascocom web wwwpascocom Contacting Technical Support Before you call the PASCO Technical Support staff it would be helpful to prepare the following information gt If 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 calling to facilitate description of individual parts gt If 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 1208Jan J O L LEVOLD r Atomic and Nuclear Physics Introductory experiments Planck s constant LE YBOLD Physics Leq ets Objects of the experiment I To verify the photoelectric effect Determining Planck s constant Selection of wavelengths with interference filters on the optical bench I To measure the kinetic energy of the electrons as a function of the frequency of the light I To determine Planck s constant h I To show that the kinetic energy of the electrons is independent of the intensity of the light Principles Electrons can be liberated from the surface of certain metals by irradiating them with light of a sufficiently short wavelength photoelectric effect Their energy depends on the frequency v ofthe incident light but not on the intensity the intensity only determines the number of liberated electrons This fact contra7 dicts the principles of classical physics and was first inter7 preted in 1905 by Albert Einstein He postulated that light consists of a flux of particles called photons whose energy E is proportional to the frequency Ehv I Fig 1 Schematic representation ofan experiment for measuring lanck s constant hwnh the aid of the photoelectric effect Monochromatic light produced by wavelength lter F falls on cathode K of a photocell The photoelectrons stimulated here travel to anode A and charge capacitor C up to the limitvoltage U0 The proportionality factor h is known as Planck s constant and is regarded as a constant of nature In this particulate concep7 tion of light each photoelectron is replaced by a photon and exits the atom with the kinetic energy Ekm h v 7 WK II where WK is the work function of the electrons It is inde7 pendent of the irradiated material We can determine Planck s constant h by exposing a photocell to monochromatic light i e light ofa specific wavelength and measuring the kinetic energy Ekm of the ejected electrons Fig 1 shows a schematic representation of such an experi7 ment The light falls through an annular anode here a platinum wire onto a potassium surface Thanks to its low work function 7 the valence electrons of alkali metals are weakly bound 7 potassium is a very suitable cathode material Some of the ejected photoelectrons travel to the anode where they are registered in the form of a photoelectric current If the photoelectrons are ejected against a negative potential which is gradually increased the photoelectric current con7 tinually decreases The voltage at which the photoelectric current reaches precisely zero is called the limit voltage U0 At this level even the electrons with the weakest bonds i e those with the lowest work function WK and thus the greatest kinetic energy can no longer overcome the anode voltage In this experiment the anode voltage is generated using a capacitor which is charged by the incident electrons up to a limit voltage U0 see Fig 1 We can use this limitvoltage U0 to calculate the kinetic energy of these weakly bound electrons III e elementary charge Here Wis no longer the work function WK of the cathode as the contact potential between the cathode and the anode is included in the energy balance P6143 LE YBOLD Physics Lea ets Apparatus 1 Photo cell for determining Planck s constant 558 77 1 Basic device for photo cel 558 791 1 High pressure mercury lam 45115 1 Lamp socket E27 on rod for highepressure mercury lam 45119 1 Universal choke in housing 230 V 50 Hz 45130 1 Lens in holder f 100 mm 46003 1 Iris diaphragm in holder 460 26 1 Filter revolver 558 792 1 Interference filter 578 nm 468401 1 Interference filter 546 nm 468402 1 Interference filter 436 nm 468 403 1 Interference filter 405 nm 468404 1 Electrometer amplifier 53214 1 Plugein unit 230 V AC12 V AC 562 791 1 STE capacitor 100 pF 630 V 57822 1 STE key switch NO 57910 1 Voltmeter DC eg 531100 1 Optical bench with standard profile 1 m 46032 or 1 Auxiliary bench w swiveljoint 05 m 460 34 2 Optics riders height 90 mm width 50 mm 460352 3 Optics riders height 120 mm width 50 mm 460357 2 Clamping plugs 590 011 1 Straight BNC 501 10 1 BNC adapter for 47mm socket 1epole 50109 1 Coupling plug 34089 1 Distribution box 502 04 Connecting leads The measurements are conducted for various wavelengths k and frequencies v IV c speed of light in a vacuum of the incident light When the frequency of the incident light increases by Av the electron energy increases by h Av The limit voltage must be increased by AUG to compensate for the rise in the photoelectric current Safety notes The high pressure mercury lamp also emits light in the UV range and can thus damage the eyes Never look into the direct or reflected beam of light from the high pressure mercury lamp Observe the Instruction Sheet for the high pressure mercury lamp When we plot the Iimitvoltage U0v as a function ofv equation Ill gives us a straight line with the slope AUo h M e V e For a known elementary charge 6 this gives us Planck s constant h In this experiment narroweband interference filters are used to select the wavelengths each filter selects precisely one spec tral line from the light of a highepressure mercury lamp The wavelength specification on the filter refers to the wavelength of the transmitted mercury line Setup Optical setup Note The highepressure mercury lamp reaches its full intensity after a teneminute warmeup period Switch on the highepressure mercury lamp when you begin setting up the experiment so that you can start measuring as soon as you are nished Fig 2 shows the experiment setup the position of the left edge of the optical riders is given in cm Connect the universal choke to the mains via the distribue tion box Mount the highepressure mercury lamp at the marked posi tion using an optical rider H 90 mm connect it to the universal choke and switch it on Mountthe photocell at the marked position using an optical rider H 90 mm remove the coverand align the photocell so that the coated black surface is facing the mercury lamp Mount the iris diaphragm on the optical bench at the marked position using an optical rider H 120 mm Mount the lens at the marked position using an optical rider H 120 mm and adjust its height so thatthe center of the lens is at the same height as the center of the iris dia phragm The light from the mercury lamp should now produce a sharp light spot on the black coating the sensitive area of the photocell The light should not fall on the metal ring nor on the part of the blackecoated area to which the contacts are at tached The edge zones should not be illuminated either To ensure that this is so carry out the following procedure repeating as often as necessary to produce the optimum image Vary the height of the iris diaphragm and the lens so that the light spot falls on the black zone of the photocell make sure that the center of the lens is always on the same level with thatof the iris diaphragm You may also need to adjust the height and inclination of the photocell using the screws below the base Using the iris diaphragm adjust the size of the light spot so that it illuminates the largest possible area of the black zone of the photocell without shining on the outer zones the metal ring or the contacts on the black coating Focus the light spotas necessary by moving the lens along the optical bench LE YBOLD Physics Lea ets P6143 Fig2 Experiment setup on the optical bench With posmons In cm for the left edge of the optical riders a high pressure mercury lamp b iris diaphragm c lens f 100 mm d revolver With interference lters e photocell Fig 3 Electrometer ampli er circuit for measuring the limit tage Note once you have adjusted the experiment setup be sure not to change the setup again Place the cover on the photocell Place the filter revolver with iris diaphragm directly in front of the photocell using an optical rider H 120 mm and connect the iris diaphragm of the filter revolver with the cover of the photo cell to prevent scattered light from reaching the photocell Electrical assembly The photoelectrons incident on the metal ring of the photocell charge a capacitor generating the limit voltage U0 required for 100pF g the kinetic energy The electrometer amplifier is used to measure the voltage at the capacitor Set up the electrometer amplifier circuit as shown in Fig 3 Attach terminal plug f and connect the 100 pF capacitor and the key switch Attach coupling plug 9 the ENC4 mm adapter and the straight BNC and connect these to the gray screened cable of the photocell Connect both black cables b of the photocell to the ground connection on the electrometer amplifier Connect the multimeter to the output of the electrometer amplifier Also Connect the plugin supply unit 12 V to the electrometer amplifier and plug it in via the distribution box Connect the optical bench and possibly the rod of the basic device of the photocell to the ground connection of the electrometer amplifier and connect this terminal to the external ground of the distribution box P6143 LE YBOLD Physics Lea ets Carrying out the experiment Notes If potassium from the lightesensitive layer of the cathode be comes deposited on the anode ring this can cause an electron ux which will interfere with the experiment If necessary bake out the photocell as described in the lnstruce tion Dirt on the photocell can cause leakage currents between the anode and the cathode which can affect the measurement of the limit voltage U0 Clean the photocell with alcohol The voltage at the capacitor can be influenced by induction effec s Move this part as little as possible during the experiment You do not need to darken the room this has no effect on the measurement results Switch on the multimeter and set the range switch to 1 V DC Turn the interference filter for yellow light ng 578 nm into the beam path Discharge the capacitor by holding down the key switch until the multimeter reads zero V Start the measurement by releasing the key switch wait about 30 s to 1 minute until the capacitor has charged to the limit voltage U0 Write down the measured value for U0 Turn the interference filter for green light ng 546 nm into the beam path and repeat the measurement Extend the measuring range to 3 V and repeat the meas urement with the blue ng 436 nm and Violet ng 405 nm interference filters Vary the intensity of the incident lightatthe photocell using the iris diaphragm ofthe filter revolver and measure the limit voltage U0 for each setting Note If the iris diaphragm is closed too far this may affect the uniform illumination of the light spot on the cathode Also leakage currents will play an increasing role Measuring example Table 1 Limitvoltage U0 as a function ofthe wavelength kand the frequency v Color Yellow 578 519 059 Green 546 549 070 Blue 436 688 123 Violet 405 741 140 Evaluation Fig 4 shows the limit voltage U0 as a function of the frequency v The plotted measurement points lie on a straight line with close approximation A line fitted to the first three measurement points has a slope of AU 003810 14 Vs Av According to V it follows from e 16 10 19 As thatthe value of Planck s constant is h 61 1034 Js Literature value h 662 10 34 Js Fig 4 Limit voltage U0 as a function of the frequency 1 Results In the photoelectric effect the kinetic energy Ekrn of the libere ated electrons depends on the frequency and not on the intensity of the incident light Planck s constant h can be determined by measuring the limit voltage U0 above which the electrons can no longer escape as a function of the frequency v LEYBOLD DIDACTIC GMBH Leyboldstrasse l D750354 Hurth Phone 02233 60470 Telefax 02233 6047222 Telex 17 223 332 LHPCGN D c by Leybold Didactic Gmbl l rinted in tne Federal Republlc of Germany Technlcal alteratlons reserved
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'