Experiments In Engineering Physics - MIT Pune
Experiments in Engineering Physics(Physics Lab Manual)Fourth (revised) editionDr. Narendra L. MathakariAssociate Professor in Physics1
“In the matter of physics, the first lessons shouldcontain nothing but what is experimental andinteresting to see. A pretty experiment is in itselfoften more valuable than twenty formulae extractedfrom our minds.”Albert Einstein2
IndexSr.noiiiiiiivContentsInstructionsThe scheme of term work assessmentHow to write the journalGeneral checklistPageno.7 and 8910101Supplementary information for Experiment 1 (Biographies of Newton and YoungExperiment 1. Newton’s ringsChecklist for Expt. 1Viva voce for Expt. 1111316172Supplementary information for Experiment 2 (Biographies of Fraunhofer and Rowland)Experiment 2. Diffraction gratingChecklist for Expt. 2Viva Voce for Expt. 2192124243Supplementary information for Experiment 3 (Biography of E.L. Malus)Experiment 3. Law of MalusChecklist for Expt. 3Viva voce for Expt. 3272931324Supplementary information for Experiment 4 (Biography of W. Sabine)Experiment 4. Sound absorption coefficientChecklist for Expt. 4Viva voce for Expt. 43335375Supplementary information for Experiment 5 (Biography of Charles Towns)Experiment 5. Laser beam divergenceChecklist for Expt. 5Viva voce for Expt. 5394145456Supplementary information for Experiment 6 (Biography of Ali Javan)Experiment 6. Laser, thin slit, wire and gratingChecklist for Expt. 6Viva voce for Expt. 64749557Supplementary information for Experiment 7 (Biography of Michael Faraday)Experiment 7. Energy gap of semiconductorChecklist for Expt. 7Viva voce for Expt. 7596164648Supplementary information for Experiment 8 (Biography of Gerald Pearson)Experiment 8. Solar cellChecklist for Expt. 8Viva voce for Expt.81656770713
Don’t forget to bring following accessorieswhile attending the lab sessionsi.ii.iii.iv.Lab manualI-CardScientific CalculatorFully equipped compass box including2-B Pencil, scale, sharpner and eraserv. Plain journal papersvi. Minimum three graph papers4
Instructions1. Attend the Lab sessions in time2. Don’t forget to bring following accessories while attending the lab sessionsi.Lab manualii.I-Cardiii. Scientific Calculatoriv.Fully equipped compass box including 2-B Pencil, scale, sharpner and eraserv.Plain journal papersvi.Minimum three graph papers3. Switch-off your cell phones when you are in the lab.4. Bags should be kept on the racks. On lab tables keep only whatever is required for theexperiment.5. Handle the instruments with due care. Note that you are fully responsible for yourapparatus in your lab session.6. In case of electronic experiments, don’t switch on the circuits unless checked by teacheror lab assistant. Operate multimeters with proper AC/DC settings & proper ranges.7. Record all your lab work in the lab manual. Get it approved & signed by teacher.8. All graphs are to be plotted in the lab itself. These can be directly attached in the journal9. Complete your practicals in regular sessions only. Avoid extra practicals.10. Complete your journals in time11. Take care of your belongings5
The scheme for Term work assessment1. The term work for Engineering Physics is for 25 marks2. There is no exam for experiments3. While assessing the term work, 60% weightage is for performing the experiments andwriting neat journals, 20% weightage is for timely submission of the journals and 20 %weightage is for theory attendance. Following methodology will be used for assessing thetermworka. Each experiment: 10 marks for performance of the experiment and for neatlywritten journal. Student attending the practical in repeat session will get lessmarksb. Eight experiments: 80 marksc. 80 marks will be converted to 60 marksd. 20 marks will be given for timely submission of the journalse. 20 marks will be given for theory attendance in the following mannerAttendance rangeAbove 90%80 % to 89 %70 % to 80 %60 % to 70 %Less than 60 %Marks out of 2020151005004. The sum of marks in step c, d and e is 60 20 20 100 marks5. 100 marks will be converted in to 25 marks6
How to write the journal The biographies of the Physicists given in the beginning of the experiment are only forinformation. Biographies are not to be written in the journal The viva is for enhancing the understanding of the experiments. Viva questions are not tobe written in the journal All rest of the matter is to be written as it is. No compromise to be made.1. The first page (and if required, the second page) should be one side ruled page.2. On ruled part start writing the experiment, (Aim, Apparatus, Significance, Theory etc.)3. The blank side of the first page (and if required, the second page) should be used fordrawing the diagrams4. Once all the diagrams are drawn, the rest of the pages should be two side ruled5. All two side ruled pages should be used for writing the remaining part of the journal6. Diagrams are to be drawn by using 2B pencil. All rest of the matter should be written bypenGeneral checklist for all the experiments1. Have you filled the front page completely? (Name, class, Batch, Subject, Experiment no,Name of the experiment, performed on (date), submitted on (date)2. Check whether you have precisely written all the contents of printed write up. Note thatyou are not permitted to reduce the contents of the write up.3. Have you given proper units to all the quantities in the observation table?4. Have you drawn all the figures precisely?5. Graph should be as per following format7
Supplementary information for Experiment 1(This page is not to be written in the journal)The concentric and circular Newton’s rings can be used for precise measurements. How?Newton was the first to observe the Newton’s ringsSir Isaac Newton (1642-1727): While the fall of an apple remains anordinary phenomenon for a layman, it was not so for Newton. The fall ofapple inspired him to formulate the universal law of Gravitation. He alsoconcluded that, the force which pulls apple down also makes Earth rotatearound Sun and Moon around the Earth. While his several contributionssuch as Mechanics, Optics and Gravitation are noteworthy, it is suffice tomention that he is claimed to be an originator of Calculus. He acquired theLucasian Professorship of Mathematics in Cambridge University, just atthe age of 26, and was elected as a Fellow of Royal Society at the age of30. In his famous book named PRINCIPIA, he published the three laws ofmotion and the Universal law of Gravitation. In another publicationnamed OPTICKS, he presented Physics of the spectrum, interference,color vision and rainbow. In 1717, he studied the circular and concentricinterference fringes known as Newton’s rings.Thomas Young was the first to explain Physics behind the Newton’s ringsThomas Young (1773-1829): ThePhysicist with versatile intelligencewas the first to demonstrate interference. He learned to read at the age of2 and said to have read the complete Bible twice at the age of 6. He was aPhysicist as well as a Physician. He made significant contributions inPhysics as well as Physiology, a few of which include understanding ofthe Physiology of Human eye, Physics of color vision, concept ofmodulus of elasticity known due to his name etc. He also gave anexperimental foundation to the wave theory of light, which was based onhis double slit experiment. In 1802, he explained Newton’s rings on thebasis of Interference.8
Experiment 1: Newton’s RingsAim: To measure the radius of curvature of a planoconex lens using Newton’s rings apparatusApparatus:(1) Newton’s rings apparatus consisting ofa. Planoconvex lensb. Optically flat glass platec. Beam splitterd. T-type traveling microscope with scale with L.C. 0.001 cm(2) Monochromatic source of light of known wavelength (ex. Sodium)(3) Reading lamp and reading lensSignificance of the experiment: Newton’s rings apparatus can be considered as aninterferometer, as it generates a steady state and well defined interference pattern. One of theprime applications of interferometers is precise measurements of dimensions. This experiment isaimed at precise measurement of radius of curvature of a plano-convex using ‘Newton’sinterferometer’. The other applications of this apparatus are measuring the wavelength ofmonochromatic source of light, refractive index of the liquids and testing preciseness of glassplates and lenses.Theory: Newton’s rings are the concentric and circular fringes obtained by using interference ofcircularly symmetric wedge shaped films. (Refer Fig. 1.1 a, b and c). Such film can be obtainedby placing a planoconvex lens on a glass plate. The region between these two components formsa circularly symmetric wedge shaped film, as the locus of points having same path differenceforms a circle. If this film is exposed to a plane wavefront of monochromatic light from the top,then the rays reflected from the top and bottom of the circularly symmetric wedge shaped filminterfere and produce Newton’s ringsBy extending the theory of wedge shaped films to Newton’s rings, it can be shown that𝑅 2 𝐷2 )𝜇(𝐷𝑚𝑛4(𝑚 𝑛)𝜆 (1.1)Where R Radius of curvature of planoconvex lensDm Diameter of mthdark ringDn Diameter of nth dark ring Wavelength of monochromatic light Refractive index of the medium inbetweenplanoconvex lens and glassplateThus if diameters of Newton’s rings are measured then a few important quantities such as R, and of the liquid can be measured.9
Fig 1.1 a: Experimental set up for observing Newton’s ringsFig 1.1c: Newton’s RingsFig 1.1b: The ray diagram for Newton’s ringsProcedure:1. Produce Newton’s rings by the procedure given below.a. Make every component dust free.b. Level the whole apparatus using spirit levelc. Keep the wooden box containing a beam splitter and glass plate below the T typemicroscope. Keep planoconvex lens on the glass plate exactly below themicroscope such that its curved part touches the glass plated. Render a parallel wavefront of sodium by placing the source at the focal length ofa lens. Expose planoconvex lens-glass plate system parallel wavefront of light.Now Newton’s rings can be seen through the microscope.e. Adjust the eyepiece of the microscope so that sharp Newton’s rings are produced10
f. If the central ring is not dark then gently tap the apparatus to make the centredark. The central ring should be dark throughout the experiment.2. The central dark ring is the zeroth one. Measure the diameters of first five dark rings byusing the procedure given belowa. Move the microscope, so that crosswire is adjusted on upper part of the first darkring. Measure this position, say P on the scale of the microscope, in the followingmannerP MSR VSR LC cmWhere MSR is the reading on main scale whichcoincides with the zero of the vernier scale. If noreading coincides, then the reading on the main saleprevious to with the zero of the vernierVSR is the sequence number of division on thevernier scale which exactly coincides with thedivision on the main scale.LC is the least count of the scale of the microscopeb. Move the microscope down to adjust the crosswire on the lower part of first darkring. Measure the corresponding position on the scale, say, Q by using theprocedure given abovec. The diameter of the ring is P – Q cmd. Repeat the above procedure for measuring the diameters of 2nd , 3rd , 4th and 5thdark rings3. Plot the graph of Dn2 Vs n. Calculate the slope of this graph. The slope gives the precise𝐷 2 𝐷 2𝑚𝑛value of ( 𝑚 𝑛)4. Calculate the radius of curvature of planoconvex lens by using formula (1.1). Takeμ 1 as Newton’s rings are produced in air. The source used is sodium, therefore take 5890 Ao 5890 10 8 𝑐𝑚5. Compare this Re with the standard radius of curvature (Rs) given. Calculate thepercentage deviation, which needs to be as less as possible.Observations:Table 1.1: Calculation of the least count of the scale on microscopeSmallest Division on the main scaleNumber of Divisions on vernier scaleL.C. of traveling microscope 0.05 cm 50 0.001 cm11
Table (1.2) Diameters of Newton’s ringsSeq. no. ofDark ring(n)12345Upper position(P), cmLower positionDiameter(Q), cmDn, P – Q cmSquare ofdiameter𝐷𝑛2 , cm2Calculations:Slope of the graph . cm2Radius of curvature of planoconvex lens2𝜇(𝐷𝑚 𝐷𝑛2 )𝑅𝑒 4(𝑚 𝑛)𝜆 1 𝑠𝑙𝑜𝑝𝑒4 5890 10 8 𝑐𝑚Standard radius ofcurvatureRs, cm50Radius of curvature usingNewton’s ringsRe , cm .𝑅𝑠 𝑅𝑒 𝑅𝑠 100 % . %% 𝑑𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛 Checklist1. In the figures, have you shown the travelling microscope on the top of the set up?2. Have you shown the calculation of radius of curvature? Have you expressed radius ofcurvature in cm?3. Have you written the result table, standard radius of curvature, experimental radius ofcurvature and percentage deviation?4. The graph should be in the following format12
Viva Voce1. Newton’s rings apparatus can be called as Newton’s interferometer. Why?2. Enlist as many interferometers, as you know.3. Comment on the nature of Newton’s rings which would be seen, if the source used werepolychromatic (white)4. Is it possible to perform this experiment with Polychromatic source? Why? Why not?5. The centre of Newton’s rings is sometimes dark and sometimes bright. What does thissignify?6. How would Newton’s rings be seen if they were observed from the opposite side i.e.from the downward direction?7. Any interferometer claims best accuracy in the measurements of various dimensions.How much was the error in your experiment? Identify the sources of errors.8. Comment on the nature of Newton’s rings that would be seen if the lens were bioconvexinstead of planoconvex.9. How would the Newton’s rings appear, if the planoconvex lens were kept in oppositemanner i.e. its curved surface up and plane surface down?10. How would the Newton’s rings be seen if the glass plate at the bottom were replaced bymirror?11. How would Newton’s rings be seen if wavefront were not parallel?12. Newton’s rings can be used to check the optical flatness of glass plates and precision ofthe planoconvex lenses. How?13
Supplementary information for Experiment 2(This page is not to be written in the journal)A well-defined and well resolved spectrum of any source can be obtained by diffractiongrating. What is diffraction grating and what are it’s uses?Fraunhofer was the first to construct diffraction gratingJoseph Von Fraunhofer (1787 -1826): He was a German Physicist.Once an undereducated apprentice, he established his own opticalindustry, where he designed and fabricated several devices andinstruments such as prisms, microscopes telescopes, astronomicalreflectors etc. In 1821, Fraunhofer described his investigations ofdiffraction patterns by diffraction gratings. He was also involved inmaking the diffraction grating. The diffraction gratings were initiallymade by winding wires around parallel screws. Using diffraction gratinghe rediscovered almost 574 dark lines in the solar spectrum, which arecalled Fraunhofer lines.Rowland developed a sophisticated technique to fabricate modern diffraction gratingsHenry Augustus Rowland (1848–1901): He was an AmericanPhysicist, who is best known for construction of Rowland machine,which is used to construct sophisticated and high quality diffractiongratings. Rowland machines are known for extraordinary trueness anddelicacy. In between 1899 to 1901, he was the president of the famousAmerican Physical Society. His contributions in Thermodynamics,Electricity and Magnetism are also noteworthy.14
Experiment 2: Diffraction GratingAim: To measure the wavelengths of spectral lines of a Mercury (Hg) source using diffractiongrating and a spectrometer.Apparatus: 1. Diffraction grating2. Spectrometer3. Mercury source (Hg)4. Spirit level5. Reading lamp and reading lensSignificance of the experiment: Diffraction grating is basically a superprism. It disperses thelight in to it’s spectrum, with dispersive power and resolving power quite higher than that ofprism. The grating assists an analytical technique called spectroscopy in the formation andanalysis of spectra.Theory: Diffraction grating is an arrangement of large number of equidistant and parallel slits(Fig 2.1). One of the techniques to manufacture diffraction grating is to rule the equidistant lineson glass plate. Typical diffraction gratings consist of 15000-20000 lines per inch (this numbercan reach up to 100000 lines per inch). The qualities i.e. dispersive power and resolving powerdepend upon number of slits and slit density.Using theory of diffraction to multiple slits, following grating equation can be derived𝑑𝑠𝑖𝑛𝜃 𝑚𝜆Where(2.1)d grating elementθ angle of diffractionm order of spectrumλ wavelength of lightIn equation (2.1), d and m are constant. This implies that θ is proportional to λ. Thus if a gratingis exposed to light from polychromatic source, the colors are separated on account of theirdifferent wavelengths. Thus diffraction grating can form the spectrum of the light. With respectto dispersive power and resolving power, grating is far better than prism. Further, if d and m areknown and if θ is measured then λ, the wavelength of spectral lines can be calculated. Due to it’sability to form well resolved spectrum and calculation of wavelengths, diffraction grating findsapplications in spectrometers. Such spectrometers (Fig 2.2) find applications in an importantdiscipline called spectroscopy, a technique extremely useful in science and technology. Eachsource has it’s own characteristic spectrum. In spectroscopy the spectra of various atomic ormolecular species are analyzed to evaluate the properties of the sources. A few applications ofspectroscopy are - understanding the structure and properties of atoms and molecules, detectionof various elements in planets and stars, study of various effects such as Zeeman effect, Ramaneffect, Stark effect etc.15
Figure 2.1: Diffraction gratingFigure 2.2: SpectrometerFigure 2.3: Definition of 2𝜃16
Procedure:1. At first calculate the grating element d of the grating by using following formula𝑑 12.542.54 108𝑖𝑛𝑐ℎ𝑒𝑠 𝑐𝑚𝑠 𝑁𝑁𝑁Where N Number of slits per inch 15000 slits per inch2. Switch on the Mercury source.3. Level the all parts of spectrometer such as telescope, collimator, grating table etc. usingspirit level.4. Bring the slit of collimator in front of spectrometer. Adjust the slit width optimum value.5. Adjust the telescope and collimator for sharp images using prism and Schuster’s method6. Mount the diffraction grating on the table such that it’s plane is exactly perpendicular tocollimator axis as well as the table7. Observe the central image of slit through telescope. This image is white, as colors can notbe separated in zeroth order. This is called as zeroth order spectrum. Make the image sharpby focusing the telescope and collimator8. Unlike prism, grating produces multiple spectra. Move the telescope on both sides of thecentral image to observe the first as well as second order spectra on both the sides of thecentral image. The second order spectrum is faint as compared to first order. So considerfirst orderspectrum for observations. Thus the order of spectrum m in Eqn (2.1) is 1. Thefirst order spectrum consists of four prominent lines namely violet, green, yellow(doublet) and red. The other relatively faint lines are purple and orange.9. Move the telescope on left hand side and adjust the cross wire on violet line. Clamp thetelescope. Measure the angular position θ1 of the violet line, by using followingprocedure𝜃1 𝑀𝑆𝑅 𝑉𝑆𝑅 𝐿𝐶Where MSR: Main scale reading: a reading on the scale which coincideswith the zero of the vernier scale. If no reading coincides then MSR is thereading on the main scale previous to zero of the vernier scale.VSR: Vernier scale reading is the sequence number of the division on thevernier scale which exactly coincides with the division on main scaleLC Least count of the angular �𝑛𝑠𝑐𝑎𝑙𝑒 (𝑋)𝐿𝐶 ��𝑖𝑜𝑛𝑠𝑜𝑛𝑡ℎ𝑒𝑣𝑒𝑟
written journal. Student attending the practical in repeat session will get less marks b. Eight experiments: 80 marks c. 80 marks will be converted to 60 marks d. 20 marks will be given for timely submission of the journals e. 20 marks will be given for theory attendance in the following manner Attendance range Marks out of 20
Physics 20 General College Physics (PHYS 104). Camosun College Physics 20 General Elementary Physics (PHYS 20). Medicine Hat College Physics 20 Physics (ASP 114). NAIT Physics 20 Radiology (Z-HO9 A408). Red River College Physics 20 Physics (PHYS 184). Saskatchewan Polytechnic (SIAST) Physics 20 Physics (PHYS 184). Physics (PHYS 182).
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General Physics: There are two versions of the introductory general physics sequence. Physics 145/146 is intended for students planning no further study in physics. Physics 155/156 is intended for students planning to take upper level physics courses, including physics majors, physics combined majors, 3-2 engineering majors and BBMB majors.
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