CHADALAWADA RAMANAMMA ENGINEERING COLLEGE (AUTONOMOUS) Chadalawada Nagar, Renigunta Road, Tirupati

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1 ENGINEERING PHYSICS LABORATORY MANUAL Subject Code : 17CA55102 Regulation : R17 Class : I B.Tech I Semester (CSE &EEE) I B.Tech II Semester (ECE &ME) CHADALAWADA RAMANAMMA ENGINEERING COLLEGE (AUTONOMOUS) Chadalawada Nagar, Renigunta Road, Tirupati Department of Freshman Engineering 1 P a g e

2 CHADALAWADA RAMANAMMA ENGINEERING COLLEGE (AUTONOMOUS) Chadalawada Nagar, Renigunta Road, Tirupati Department of Freshman Engineering Name Reg.No. Branch/Section Academic year 2 P a g e

3 INDEX S. No Name of the Experiment Page No 1 Determination of thickness of thin object using wedge method Determination of wavelength different colors of given mercury source using diffraction grating in normal incidence method Determination wavelength of laser source using diffraction grating Determination of particle size using diffraction Determination of Numerical aperture, acceptance angle of an optical fiber Energy gap of a Semiconductor diode Determination of radius of curvature of a Plano-convex lens by forming Newton s rings Hall effect Determination of mobility of charge carriers B-H curve Determination of hysteresis loss for a given magnetic material Determination of dispersive power of a prism Study of CRO measurements LED and LASER characteristics Field along the axis of coil carrying current Stewart Gee s method Determination of Planck s constant using LED P a g e

4 Introduction Engineering Physics is an experimental science. The main aim of engineering physics is to give fundamental knowledge of science and technology for engineering students. The study of Engineering Physics emphasizes the application of basic scientific principles to the design of equipment, which includes electronic and electro-mechanical systems, for use in measurements, communications, and data acquisition. The theory that is presented in lectures has its origins in, and is validated by, experimental measurement. The practical aspect of Physics is an integral part of the subject. The laboratory practicals take place throughout the semester in parallel to the lectures. They serve a number of purposes: It is an opportunity, as a student, to test theories by conducting meaningful scientific experiments. It is useful to enrich and deepen understanding of physical concepts presented in lectures. It is helpful to develop experimental techniques, in particular skills of data analysis, the understanding of experimental uncertainty, and the development of graphical visualization of data. Students are advised to thoroughly go through this manual rather than only topics mentioned in the syllabus as practical aspects are the key to understanding and conceptual visualization of theoretical aspects covered in the books. Objectives: The objective of the laboratory is learning. To measure the different wavelengths different colours. To understand the role of optical fiber parameters and signal losses in communication. To recognize the importance of energy gap in the study of conductivity and hall effect in a semiconductor To understand the applications of B H curve. To acquire a practical knowledge of studying the crystal structure in terms of lattice constant. To recognize the application of laser in finding the particle size and its role in diffraction studies. To learn to synthesis of the nanomaterials and recognize its importance by knowing its nano particle size and its impact on its properties. Out comes: To recognize the importance of optical phenomenon like Interference and diffraction. To acquire the practical application knowledge of optical fiber, semiconductor, dieclectric and magnetic materials, crystal structure and lasers by the study of their relative parameters. To recognize the significant importance of nanomaterials in various engineering fields. 4 P a g e

5 Instructions to the students: The following instructions must be followed by the students in their laboratory classes. 1. Students are expected to be punctual to the lab classes. If they are late, they will be considered absent for that particular session. 2. Students should strictly maintain the dress code. 3. Students must bring their observation note, record note (completed with previous experiment) and the calculator, scales, pencils to every lab class without fail. 4. Students are advised to come with full preparation for their lab sessions by (i) (ii) Reading the detailed procedure of the experiment from the laboratory manual. Completion of observation note book (i.e.) Aim, Apparatus required, Formula (with description), least count calculation, diagrams and the tabular column should be written in the observation note before entering into the laboratory. 5. Data entry in the observation note book must be by pen only. 6. Bring necessary graph papers for each of experiment. Learn to optimize on usage of graph papers. 7. Graphs should be neatly drawn with pencil. Always label graphs and the axes and display units. 8. If you finish early, spend the remaining time to complete the calculations and drawing graphs. Students must get attestations immediately for their observed readings. 9. Students should complete their calculations for their experiments and get it corrected on the same day of that experiment. 10. Students who miss observation, record note they have to do the experiment once again and get it corrected. 11. Class assessment marks for each experiment is based only on their performance in the laboratory. 12. Record note has to be completed then and there and get corrected when the students are coming for the next lab class. 13. Students must strictly maintain silence during lab classes. 14. If any of the students is absent for the lab class for genuine reasons, he/she will be permitted to do the experiment during the repetition class only. 15. Students are advised to perform their experiments under safety care. 16. If any student is found causing damage to the lab equipments, he/she shall replace the same with a new. 5 P a g e

6 CHADALAWADA RAMANAMMA ENGINEERING COLLEGE, TIRUPATI (AUTONOMOUS) Syllabus for (R17 Regulations) ENGINEERING PHYSICS LABORATORY (17CA55102) (Common to All Branches) Any 10 of the following experiments has to be performed during the I year I/II semester 1. Determination of thickness of thin object using wedge method. 2. Determination of wavelength different colors of given mercury source using diffraction grating in normal incidence method. 3. Determination wavelength of laser source using diffraction grating. 4. Determination of particle size using diffraction. 5. Determination of Numerical aperture, acceptance angle of an optical fiber. 6. Determination of radius of curvature of a Plano-convex lens by forming Newton s rings. 7. Hall effect Determination of mobility of charge carriers. 8. B-H curve Determination of hysteresis loss for a given magnetic material. 9. Determination of dispersive power of a prism. 10. Energy gap of a Semiconductor diode. 11. Study of CRO measurements. References: 1. Engineering Physics Practicals NU Age Publishing House, Hyderabad. 2. Engineering Practical physics Cengage Learning, Delhi 6 P a g e

7 Expt. No: Date: EXPERIMENT 1 TO FIND THIKNESS OF A THIN OBECT USING WEDGE METHOD 1.1 AIM: To determine the thickness of a thin object or wire or hair by forming parallel fringes using wedge method. 1.2 APPPRATUS: S. No Equipment Range Type Quantity 1 Sodium vapor lamp - Standard 1 2 Traveling microscope - Standard 1 3 Thin wire or hair or small piece of paper - Standard 1 4 Reading lens - Standard 1 5 Plane glass plates - Standard FORMULA: The Thickness of wire or hair can be found using the following formula. t = λ L/2β cm where, λ = Wavelength of light source (cm). L = Distance between wedge to hair (cm). β = Fringe width (cm). 1.4 PROCEDURE: a. The experimental arrangement for producing parallel fringes is as shown in fig (1). b. Two plane glass plates are taken. They are cleaned thoroughly. They are held in contact at one edge. At the opposite edge, a thin paper is inserted between the glass plates. The air-wedge is formed between the lower surface of upper and upper surface of lower glass plate. c. This set up is carefully kept on black paper and placed on the plat form of traveling microscope. d. Arrange the glass plate B at an angle of 45 0 over the base set. e. Switch on the monochromatic light source and it is focus on the Double convex lens (L1). This sends parallel beam of light. This beam of light falls on the glass plate B at 45 0 f. The glass plate B reflects a part of light towards the air film enclosed by the glass plates. g. The microscope is adjusted and focused until the parallel fringes are formed. h. Starting from one side coincide the cross wires tangential to the parallel fringes and note the reading for every 5 fringes (0 th, 5 th, 10 th, 15 th, 20 th, 25 th ). i. Calculate the fringe width β. j. Measure distance between wedge to hair (L) using the scale. k. The thickness of wire is calculated by using the formula: t = λl/2β cm. 7 P a g e

8 1.5 TABULAR COLUMN: Fig: Arrangement and formation of parallel fringes. TABLE -1 Least count (L.C) of traveling microscope = cm Microscope readings MSR VSCXLC S.No Ring No. VSC (a) cm (b) cm 1 0 T = (a+b) cm TABLE -2 S.No Fringe Number Microscope Reading (A) cm Fringe Number Microscope Reading (B) cm Fringe Width 5β = (A~ B) cm Avg β = cm β = cm 8 P a g e

9 1.6 PRECAUTIONS: 1. The microscope should move in one direction from left to the right or right to left, so he back lash error is avoided 2. To achieve good accuracy in the measurement of l should be repeated twice or thrice. 3. The glass plate should be perfectly plane. 4. The wire should be uniform. 1.7 OBSERVATIONS: 1. The distance of the object from edge of the wedge L = (cm), 2. Fringe width β= (cm) 3. Wavelength of source λ =5893X10-8 cm 1.8 RESULT: Thickness of the thin wire is determined by using Interference by parallel fringes is..cm. 1.9 PRELAB VIVA QUESTIONS: 1. What is Interference? What are the conditions for interference? 2. Explain constructive & Destructive interference. 3. What is meant by monochromatic source? 4. What is the wavelength of sodium vapour lamp? 5. Define Path difference& Phase difference and give relation b/w them. 6. If any light ray reflected by the denser medium, what happens to its phase? 1.10 POSTLAB VIVA QUESTIONS: 1. What is the least count of travelling microscope? 2. Why we get the fringes in the shape of parallel? 3. What is the principle of wedge method? 4. What is the application of wedge method? 5. What is thin film? 6. What are examples of natural thin films? 9 P a g e

10 Expt. No: Date: EXPERIMENT 2 TO FIND WAVELENGTHS OF DIFFERENT COLORS OF MERCURY SOURCE USING DIFFRACTION GRATING NORMAL INCIDENCE METHOD 1.1 AIM: To determine the wavelengths of different colors of a given mercury vapor lamp by using the diffraction grating in normal incidence position. 1.2 APPARTUS: S. No Equipment Range Type Quantity 1 Mercury vapor lamp - Standard 1 2 Spectrometer - Standard 1 3 Diffraction grating 15,000LPI Standard 1 4 Reading lens - Standard 1 5 Spirit level - Standard FORMULA: The wavelengths of different colors of mercury vapor lamp can be found using the formula λ = sinθ Nn A0 where, θ is the diffraction angle. 1.4 PROCUDURE: The usual initial adjustments of the spectrometer are done. The least count of the vernier of the spectrometer is found Normal Incidence: a. The slit of the spectrometer is illuminated with mercury vapor lamp. b. The telescope is placed in line with the axis of the collimator and the direct image of the silt is observed. c. The slit is narrowed and the vertical cross wire is added to coincide with the center of the image of the slit (T1 from fig a) the reading of one of the vernier is noted. d. The prism table is clamped firmly and the telescope turned through 90 0 and fixed in position.(t2 in fig ). e. The grating is held with the rulings vertical and mounted in its holder on the prism table such that the plane of the grating passes through the center of the table and the ruled surface towards the collimator. 10 P a g e

11 f. The prism able is released and rotated until the image of the slit is seen in the telescoped by reflection on the ruled sided of the grating. g. The prism table is fixed after adjusting the point of intersection of the cross wires is on the image of the slit. h. Then the vernier table is released and rotated through exactly 45 0 from the position so that the ruled side of the grating faces the collimator. i. The vernier table is fixed in the position and the telescope is brought back to the direct reading position. Now the light from the collimator strikes the grating normally Measurement of wavelength (λ): a. The telescope is rotated so as to catch the first order directed image on one side, say on the left (fig. b). b. The point of intersection of the cross wires is set on the consider color line and its readings is noted on both the vernier scales. c. Similarly the reading corresponding to the remaining color lines is noted. d. Then the telescope is turned to the side i.e., right side and similarly the readings corresponding to color lines of the first order spectrum are noted. e. Half the difference in the readings corresponding to any one line gives the angle of diffraction (θ) for those lines in the first order spectrum.the number of lines per cm. of the grating (N) is noted and the wavelength of the spectral line (λ) is found by the relation, λ = sinθ Nn A0. 11 P a g e

12 1.5 TABULAR COLUMN: Order of spectrum (n) =1 S.No Color (Left Side) TABLE -1 MSR VSC VSCXLC MSR+VSCXLC 1 Blue VA VB 2 Green 3 Yellow 4 Red VA VB VA VB VA VB S.No Color (Right Side) TABLE -2 MSR VSC VSCXLC MSR+VSCXLC 1 Blue 2 Green 3 Yellow 4 Red VA I VB I VA I VB I VA I VB I VA I VB I 12 P a g e

13 TABLE -3 Readings of Spectrometer θ S.N o. Colour Left side 1 st order Left Right VA VB Right side 1 st order Left Right VA 1 VB 1 VA VA 1 (x 1 ) VB VB 1 (x 2 ) Mean 2θ= (X 1 +X 2 ) 2 λ = sinθ Nn A0 1 Blue 2 Green 3 Yellow 4 Red 1.6 OBSERVATIONS: Number of lines per cm on the grating N = 2500 lines /inch = 2500lines/ 2.54cm [1 inch =2.54 cm] = lines/ cm 1.7 PRECAUTIONS: a. Always the grating should be held by the edges. The ruled surface should not be touched. b. Light from the collimator should be uniformly incident on the entire surface of the grating. c. Spectrometer readings should take perfectly. 1.8 RESULT: The wavelengths of different colors in a given source of light are determined by using the diffraction grating in the normal incidence position. S.NO. Colour Experimental Wavelengths( A 0 ) Standard wavelengths( A 0 ) 1 Violet Indigo Blue Green Yellow Orange Red P a g e

14 1.9 PRELAB VIVA QUESTIONS: 1. What is meant by diffraction of light? 2. What is grating? 3. How does the grating form diffraction images when monochromatic light falls normally on it? 4. What is the difference B/w diffraction & refraction? 5. What are the standard wavelengths for different colors? 1.10 PRELAB VIVA QUESTIONS: 1. What is a Grating element &how its value is calculated? 2. What is the formula to calculate N on the grating? 3. What is the grating element in your experiment? 4. Is there any difference between the standard wavelengths and obtained wavelengths? 5. What is the least of spectrometer? 14 P a g e

15 Expt. No: Date: EXPERIMENT 3 TO FIND WAVELENGTH OF LASER SOURCE USING DIFFRACTION GRATING 1.1 AIM: To determine wavelength of laser beam by using a diffraction grating. 1.2 APPRATUS: S. No Equipment Range Type Quantity 1 Laser source (diode laser) - Standard 1 2 Diffraction grating 2,000LPI Standard 1 3 Optical bench - Standard 1 4 Meter graph - Standard 1 5 Meter scale - Standard FORMULA: The Wavelength of a laser λ= Sin θ 1.4 FIGURE: where, N n cm. θ = angle of diffraction n = Order of the diffraction. N = No. of lines on the grating per cm. Fig. 1 Experimental arrangement of a laser source -Diffraction grating. 1.5 PROCEDURE: a. Arrange laser source, diffraction grating and screen rectilinearly at the same height on the optical bench. b. Keep the distance (D) between the grating the screen at fixed value (say 20cm). c. Switch on the laser source then the laser beam incident normally on the surface of the grating. 15 P a g e

16 d. Then the laser gets diffracted from the ruled surface of the given grating and formed diffraction pattern on the screen. e. We can observe different diffraction orders of the bright spots on the screen on either side of the central maximum. f. Let the distance from the central maximum to diffracted spot on the left side is d1 and that on the right side is d2. g. The average of the d1 and d2 is d. h. The wave length of the given source can be determined by using this formula. i. Repeat the experiment values (D=30, 40, 50cm ) and note the corresponding d values for different diffraction orders and tabulate the readings. 1.6 TABULAR COLUMN: TABLE - 1 S. No Distance between grating and screen (D) cm Order of diffraction Distance of the diffracted spot from central spot from central maxima (cm) Left side d1 cm Right side d2 cm Mean (d= d 1+d 2 )cm 2 θ =Tan -1 ( d D ) λ= Sin θ N n cm. n=1 1 n=2 n=1 2 n=2 n=1 3 n=2 1.7 OBSERVATIONS: Number of lines per cm on the grating N = 2500 lines /inch = 2500lines/ 2.54cm [1 inch =2.54 cm] = lines/ cm. 1.8 RESULT: The wave length of the given source (λ) is 16 P a g e

17 1.9 PRELAB VIVA QUESTIONS: 1. What is laser? What are the characteristics of laser? 2. What are the differences of laser source and ordinary source? 3. What is diffraction? 4. What are the differences between interference and diffraction? 1.10 POSTLAB VIVA QUESTIONS: 1. What is the wavelength of diode laser? 2. Is the laser source is highly directional and intense? 3. Is the laser light is monochromatic? 17 P a g e

18 Expt. No: Date: EXPERIMENT 4 TO FIND SIZE OF A PARTICLE USING DIFFRACTION GRATING 1.1 AIM: To determine the size of tiny particles (in lycopodium powder) using a diffraction grating. 1.2 APPRATUS: S. No Equipment Range Type Quantity 1 Laser source (diode laser) - Standard 1 2 Glass plates - Standard 2 3 Lycopodium powder - Standard 1 4 Graph paper - Standard 1 5 Scale - Standard FORMULA: The Size of the particle is d = 1.22nλD r Where, λ = Wavelength of a laser light (cm), cm D = Distance between glass plate and screen (cm), r = Distance of the first dark fringe from the central maximum or radius of the first dark fringe (cm) and n = Order of diffraction Fig: Experimental arrangement 18 P a g e

19 1.4 PROCEDURE: 1. Arrange the diode laser, collimating lens, glass plate containing marble powder and screen rectilinearly on an optical bench at the same height. 2. Collimate the lens in front of the laser source such that the glass plate should be exactly at the focal point of the collimating lens. 3. Switch on the laser source and allow the laser light to incident on the glass plate normally. 4. The laser light can be diffracted at the edges of the marble particles. 5. Then we can observe the diffraction pattern in the form of fringes with central maximum on the screen. 6. Then adjust the distance between the glass plate and the screen such that the first dark fringe coincides with the first ring on the screen. 7. Measure the distance of the first dark fringe from the central maximum and also the distance between glass plate and screen. 8. The size of the particle can be found by using this formula. i.e.,d= 1.22 nλ D/ r cm. 9. Repeat the experiment for the first dark fringe to coincide with different circles on the screen and note the corresponding r and D values 10. The readings are tabulated as shows in the given table. TABLE S.No Distance between particle deposited glass plate and the screen D(cm) Order of diffraction (n) 1 n =1 n =2 2 n =1 n =2 3 n =1 n =2 4 n =1 n =2 Radius of the first dark fringe r (cm) d = 1.22nλD r cm Observations: Wave length of the laser λ= 6900x10-8 cm Ave=..cm 19 P a g e

20 RESULT: The size of the given particle (marble powder) is (d)= cm VIVA-VOCE QUESTIONS: 1. Define diffraction. What are conditions of diffraction 2. Define laser and what are the characteristics of laser? 3. What are the differences between interference and diffraction? 4. What is wavelength? 5. What is diffraction? 6. Define laser. 7. What are the characteristics of laser? 20 P a g e

21 Expt. No: Date: EXPERIMENT 5 8. TO FIND NUMERICAL APERTURE AND ACCEPTANCE ANGLE OF OPTICAL FIBER 1.1 AIM: To determine the acceptance angle and numerical aperture of an optical fiber. 1.2 APPRATUS: S. No Equipment Range Type Quantity 1 Fiber optic light source - Standard 1 2 Optical fiber cables - Standard 1 3 Numerical aperture jig - Standard 1 4 Optical bench - Standard FORMULA: Numerical aperture (N.A) = sin (θa) = Acceptance angle (θa) = sin -1 (NA) where W 4L2+W2 θa Acceptance angle in radian= S, W Diameter of the circular image in cm, L Distance from the fibre end to circular image in cm. 1.4 THEORY Numerical Aperture is defined as the light gathering capability of the fiber Mathematically given by: NA= Sin θ A Fig : Numerical Aperture measurement. 21 P a g e

22 1.5 PROCEDURE 1. The experimental set up for N.A.measurement is shown in fig. 2. One end of optical fiber connected to the fiber optic light source and the other end of the fiber is connected to the Numerical aperture jig through the connecter. 3. The A. C main is switched on. The light emitted by LED passes through the optical fiber cable to the other end. 4. Now, we get illuminated circular patch on the screen. 5. A screen with concentric circles of known diameter is moved along the length of the NA jig to 0bserve the circular spreading of light intensity on the screen. 6. The screen adjusted such that, the first circle from the center of the screen is completely filled with light. At this position, the distance (L) from the fiber end to the screen is noted on the NA jig. 7. The experiment is repeated for the subsequent circles by adjusting the length L along NA jig and the readings are noted in table (1). The diameter of the circles may be determined using a traveling microscope. 8. Numerical aperture and acceptance angle of cable is found by using the formula. s.no Diameter of the Circular image w cm TABLE Distance from the fibre end to circular image L cm (N.A) = sinθa W = 4L2+W2 (θa) = sin -1 (NA) 1 5mm= 0.5cm 2 10mm= 1cm 3 15mm=1.5cm 4 20mm=2cm 5 25mm=2.5cm 6 30mm=30cm 1.6 RESULT Numerical aperture of given optical fibre = Acceptance angle of the optical fibre = VIVA-VOCE QUESTIONS 1. What is an optical fiber? 2. What is total internal reflection? 3. What is acceptance angle? 4. What are applications of optical fibers? 22 P a g e

23 Expt. No: Date: EXPERIMENT 6 9. TO FIND RADIUS OF CURVATURE OF PLANO-CONVEX BY FORMING NEWTON S RINGS 1.1 AIM: To observe Newton rings formed by the interference and to determine the radius of curvature of a planoconvex lens. 1.2 APPRATUS: S. No Equipment Range Type Quantity 1 Travelling microscope - Standard 1 2 Plano-convex lens - Standard 1 3 Sodium vapour lamp - Standard 1 4 Glass plates - Standard 2 5 Magnifying lens - Standard FORMULA: The Radius of curvature of given plano-convex Lens is given by where R = D n 2 D m 2 4 (n m) λ cm λ = wavelength of sodium vapor lamp) = 5893A 0 =5893x 10-8 cm D 2 n =Diameter of n th Ring (cm) D 2 m = Diameter of m th Ring (cm) 1.4 THEORY: The phenomenon of Newton s rings is an illustration of the interference of light waves reflected from the opposite surfaces of a thin film of variable thickness. The two interfering beams, derived from a monochromatic source satisfy the coherence condition for interference. Ring shaped fringes are produced by the air film existing between a convex surface of a long focus plano-convex lens and a plane of glass plate. When a plano-convex lens of long focal length is placed on a plane glass plate, a thin film of air is enclosed between the lower surface of the lens and upper surface of the glass plate. The thickness of the air film is very small at the point of contact and gradually increases from the center outwards. The fringes produced are concentric circles. With monochromatic light, bright and dark circular fringes are produced in the air film. When viewed with the white light, the fringes are colored. A horizontal beam of light falls on the glass plate at an angle of The plate B reflects a part of incident light towards the air film enclosed by the lens and plate. The reflected beam from the air film is viewed with a 23 P a g e

24 microscope. Interference takes place and dark and bright circular fringes are produced. This is due to the interference between the light reflected at the lower surface of the lens and the upper surface of the plate. 1.5 PROCEDURE Fig. 1 Experimental set up Fig. 2 formation Newton s rings 1. The experimental arrangement for producing Newton rings is as shown in Fig Keep the convex surface of the lens (P) over the glass plate G and arrange glass plate G at an angle of 45 0 over the base set (Fig 1). 3. Switch on the monochromatic light source and it is focus on the double convex lens (L). This sends parallel beam of light. This beam of light falls on the glass plate G at The glass plate G reflects a part of light towards the air film enclosed by the lens (P) and the glass plate (E). 5. A part of the light is reflected by the curved surface of the lens and a part is transmitted which is reflected back from the plane surface of the glass plate. 6. These reflected light rays superimpose with each other producing interference and forming interference and forming interference patterns in the form of bright dark circular rings. 7. These rings are seen with a travelling microscope (M) focused on the air film. 8. Now move the microscope to focus on a dark ring (say, the 20 th order dark ring) on left side from the center. Set the cross wire tangential to one ring as shown in fig. Note down the microscope readings. 9. In the similar way cross wire setting at 14 th, 12th nd dark ring, the readings are noted. The microscope is moved in the same direction to the other side of the ring and the readings are noted corresponding to the 2 nd, 4 th, 8 th, 10 th, th dark ring on right side. 24 P a g e

25 TABLE S.No Ring No. (n) Left side Microscope reading Right side Diameter MSR (a) VSR (b) TR(cm) A=(a+b) MSR (a) VSC (b) TR(cm) B=(a+b) D(cm) A~B D 2 (cm 2 ) Average: D 2 n - D 2 m=. cm GRAPH A graph is drawn with the number of rings on the x- axis and the square of the diameter of the ring (D 2 ) on the y-axis. The graph is straight line passing through the origin. Form the graph the values of Dm 2 and Dn 2 corresponding to n th and m th rings are found. From the graph, the slope is calculated. After evaluating the slope, radius of curvature of Plano Convex lens can be calculated. 25 P a g e

26 1.6 PRECAUTIONS 1. When circular rings are formed don t disturb the total arrangement. 2. Microscope readings must take perfectly. 3. After completion of Experiment, we switch off the Na lamp Transformer. Otherwise, due to heat it may breaks. 4. The Plano-convex lens should be of large radius of curvature. 5. The centre of the ring system should be a dark spot. 6. The microscope is always moved in the same direction to avoid back lash error. 1.7 RESULT The radius of curvature of given plano convex lens is found. From the Experiment R = cm. From the Graph R = cm. VIVA-VOCE QUESTIONS 1. What is Interference? What are the conditions for interference? 2. Explain constructive & Destructive interference? 3. What is the least count of travelling microscope? 4. If we filled water between plane glass plate and the lens, what happen to the diameters of rings? 5. Define Path difference& Phase difference? Give relation between them? 6. If any light ray reflected by the denser medium, what happens to its phase? 7. Why we get the fringes in the shape of circles? 8. What is the principle of Newton rings? 9. What are the applications of Newton rings? 10. What is thin film? 11. What are examples of natural thin films? 26 P a g e

27 Expt. No: Date: 1.1 AIM: EXPERIMENT TO DETERMINE THE HALL COEFFICIENT, THE CONCENTRATION OF THE MAJORITY CARRIERS, THE MOBILITY OF THE CHARGE CARRIERS The objectives of the experiment are 1) To determine the Hall coefficient 2) To determine the concentration of the majority carriers 3) To determine the mobility of the charge carriers 1.2 APPRATUS: S. No Equipment Range Type Quantity 1 The extrinsic semiconductor material - P- Type 1 2 constant current source - Standard 1 3 electro-magnets - Standard 1 volt meter having high input 4 impedance - Standard INTRODUCTION: If magnetic field is applied among X-direction and current is applied along Y-direction, then the voltage will be developed perpendicular to the both current and magnetic field direction i.e. in Z-direction.This effect is known as Hall effect and developed voltage is called Hall voltage. The schematic demonstration of Hall Effect is known in fig P a g e

28 1.3 THE0RY: Take a p-type semiconductor wafer of thickness t and area of cross-section A. It carriers a current I is acted upon by a transverse magnetic field B. The magnetic field deflect carriers in a semiconductor wafer towards the one of the faces leading to an accumulation of charge carriers. This will produce an electric field EH in a direction which opposes the Lorentz force due to magnetic field. The electric field which builds will be exactly balances the electric field. The potential difference VH arising due to EH is given by VH=BI/ ρet Thus RH =1 / ρe ; RH =VH t / BI Slope =ΔVH /ΔI Slope =ΔVH /ΔB Where B is the magnetic field I is the current, VH is the Hall voltage. The ratio is known as Hall coefficient RH. Thus RH1 = [ Slope * (t/b )] RH2 = [ Slope * ( t / I )]. Hall coefficient (RH) is given by RH=[ RH1 +RH2] /2 m 3 /c (1) If we know the thickness t of the semiconductor wafer, the magnetic field B and by measuring the Hall voltage VH produced in the wafer for given current I, the Hall coefficient RH can be determined with the help of equation (3). If we know the Hall coefficient, the concentration of charge carriers in the material can be determined with the help of equation (1). Majority carrier concentration n (or) ρ = 1 / (RH *e ) (2) Conductivity (σ) is given by σ = 1 / ρ (3) Mobility of charge carriers (µ) = σ * RH m 2 /vs (4) Knowing the conductivity of the semiconducting material, the mobility of charge carriers in the material can be obtained from the following relation. 1.5 DESCRIPTION EXPERIMENT SETUP: The apparatus consists of a constant current source and digital panel meter. The current flowing through the semiconductor and voltage developed can be read with the help of current meter and volt meter. The semi conductor is taken in the form of a wafer and mounted on a strip. Four contacts were soldered on the wafer. An electro magnet supplies uniform magnetic field. The magnetic field can be directly read from the panel meter located on the power supply unit.the strength of the magnetic field can be varied with the help of a potentiometer. The circuit diagram for the measurement of Hall voltage is shown in figure P a g e

29 1.6 PROCEDURE: 1) The semiconductor is mounted on the probe strip and four electrical contacts re provided on the strip. The circuit is connected as shown in figure 2. The lengthwise contacts are connected to current meter and breadth wise contacts are connected to voltmeter. 2) The probe is placed in the gap of the electromagnets which provides magnetic field in direction perpendicular to the current direction and adjusts the magnetic field to suitable value and keep constant. 3) The current through the semiconductor is adjusted to suitable value with te help of constant current source and corresponding voltage polarity can be noted. 4) For different current values, the corresponding Hall voltage developed can be noted down with the help of voltmeter and the results tabulated in table 1. 5) Now keep the current value constant at a constant value and the magnetic field is varied in steps of 500 gauss, at each set of magnetic field note down the corresponding Hall voltage. The observations are tabulated in table 2. 6) Using the above observations plot the graphs. In one graph plot the current versus voltage at a constant magnetic field. In second graph magnetic field versus Hall voltage. In both the cases the graphs will be straight lines. TABLE: 1: At constant magnetic field ( B) = 2.5 gauss S.NO CURRENT (I) ma HALL VOLTAGE (VH) mv At constant current (i) = 2.5 amp TABLE: 2: S.NO MAGNETIC FIELD (B) gauss HALL VOLTAGE (VH) mv Model graphs: (1) Variation of Hall voltage with current (2) Variation of Hall voltage with magnetic field Voltage(mv) Voltage(mv) Current(mA) Magnetic field (B) 29 P a g e

30 1.8 PRECAUTIONS: 1) Care should be taken to limit the current through the probe to a value less than that of its capacity 2) The probe should be properly centered and mounted in the magnetic field so that maximum voltage is generated. 3) The potentiometer control of electro magnet is kept at a minimum value while switching on or off of the power supply. 4) The potentiometer control of the current flow through the probe is also brought to zero while switching on or off the current source. 5) Magnetic field should be varied gradually and slowly to avoid damage to the electromagnetic cols. 1.9 RESULT: 1) The Hall voltage measured (RH) = m 3 /c 2) The mobility of charge carriers ( µ ) = m 2 /vs 3) The Majority carrier concentration ( n or ρ )= /m 3. VIVA-VOCE QUESTIONS 1) What is the application of the Hall Effect? 2) Why did Hall utilize the thin gold foil to do the experiment? However, the sample we utilize in this experiment isn't necessarily thin? 3) Based on your experimental result, what is difference between n-type & p-type germanium Halleffect wafers? 4) What do the red and black inks onthe samples represent? n-type or p-type germanium Hall Effect wafers? Explain how you can make the conclusion. 30 P a g e

31 Expt. No: Date: EXPERIMENT 8 TO DETERMINE THE HYSTERESIS LOSS IN THE TRANSFORMER CORE USING B-H CURVE UNIT. 1.1 AIM: To determine the hysteresis loss in the transformer core using B-H curve unit. 1.2 APPRATUS: S. No Equipment Range Type Quantity 1 B-H-Curve unit - Standard 1 2 CRO - Standard 1 3 Patch cards - Standard FORMULA : Energy loss = N1 R2 C2 SV SH Area of the loop (Joules / cycle ) / unit volume. N2 R1 A1 Where N1=number of turns in the primary coil= 200 turns. N2=Number of turns in the secondary coil=100 turns. Circumference of the coil = 2πr =30 cm [since 1 m = 100 cm ] r = 30 / 2π = 15/ π [1cm = 1/100 m = 1/10 2 m ] r2 = (15/ π ) 2 = 225 / π2 [1cm = 10 mm] A1= πr 2 = π (225 / π2 ) = 225/(22/7) =225 /3.14 = Cm 2 = χ10-4 m 2 A 1= Area of cross section of core = χ10-4 m 2. L= length of the core SV= Vertical sensitivity of the CRO SH= Horizontal sensitivity of the CRO C2 = 4.7 χ10-6 F. R1= 0.1 Ω R2 = 680 Ω 1.4 DESCRIPTION: The experimental arrangement is shown in Figure. One of the specimen used in the unit is made using transformer stampings. There are two windings on the specimen (primary and secondary). The primary is fed to low A.C voltage (50 Hz). This produces a magnetic field H in the specimen. The voltage across R1 (resistance connected in series with primary) is proportional to the magnetic field. It is given to the input of the CRO. The A.C. magnetic field induces a voltage in the secondary coil. The voltage induced is proportional to db/dt. This voltage is applied to passive integrating circuit. The output of the integrator is proportional to B and fed to the vertical input of the CRO. As a result of the application of voltage proportional to H the horizontal axis and a voltage proportional to B is the vertical axis, the loop is formed as shown in figure. 31 P a g e

32 1.5 PROCEDURE : The unit one to force te B-H loop of the ferromagnetic specimen using a CRO is shown in Fig. A measurement of area of the loop leads to the evaluation of energy loss in the specimen. The top view of the unit is shown in figure. There are 12 terminals on the panel, sin patch cards are supplied with kit. The value of R1 can be selected connecting terminal D to B or C. (A-D=50 ohm; B-D=150 ohm; C-D=50 ohm) A is connected to D. The primary terminals of the specimen is connected to p, p secondary to s, s terminals. The CRO is clibrated as per the instructions given in the manual of CRO. CRO is adjusted to work on external mode (the time base is switched off). The horizontal and vertical position controls are adjusted such that the spot is at the centre of the CRO screen. The terminal marked GND is connected to the ground of the CRO. The H is connected to the Horizontal input of the CRO. The power supply of the unit is switched on. The hysteresis loop is formal. The horizontal and vertical gains are adjusted such that the loop occupies maximum area on the screen of the CRO. Once this adjustment is made, the gain controls should not be disturbed. The loop is traced on a translucent graph paper. The area of the loop is estimated. The connections from CRO is removed without disturbing the horizontal and vertical gain controls. The vertical sensitivity of the CRO is determined by applying a known A.C voltage say 1 volt (peak to pak). If the spot deflects by X cms for 1 volt, the vertical sensitivity is 1/x 10-2 (volt/m). Let it be dv. The horizontal sensibility of CRO is determined by applying a known A.C. voltage say 1 volt (peak to peak). Let the horizontal sensitivity be SH (volt/m) The transformer core may be replaced by ferrite ring and hysteresis loss in ferrite core can be found. TABLE : S.NO 1. CH1 V/S CH2 V/S SV cm SH cm Area of loop(mm) Energy loss(j/c/m 3 ) RESULTS: Energy loss =.Jouls cycle -1 m -3. VIVA-VOCE QUESTIONS 1. What is susceptibility? 2. What is magnetization and how it can be achieve? 3. Does an atom with one electron in outer shell can behave like a bar magnet? or simply does an atom can be equivalent to the bar magnet? 4. What is atomic dipole? 32 P a g e

33 5. How to find the atomic dipole element? 6. What is magnetic field induction and magnetic field intensity, how you will define it and what is the relationship between them? 7. How do you see magnetic field density in a region of magnetic field by bar magnet? 8. What is the unit of magnetic field induction (density) and magnetic field intensity and from which letters we represent to them? 9. What is the role of external magnetic field in magnetization of the material, how atomic dipole moments of atoms plays the role in the magnetization? 10. Can you explain the types of magnetic material (Diamagnetic, Paramagnetic, Ferromagnetic, Antiferromagnetic) on the basis of atomic dipole moments? 11. In which unit you measure the magnetic field intensity H, meniscus height h in your observation? 12. Does you have plot the graph between h and H^2, if yes where you will use the slope of this graph and why? 13. In which unit system you calculated the value of susceptibility, SI or CGS? 14. What is g in the susceptibility formula and unit of it? 15. What is Gauss Probe and for what purpose we use it? 16. What is an electromagnet, how do we use it to magnetize the material? 17. Why the FeCl3 liquid in Quinke s tube rise or fall in the presence of external magnetic field? 18. Does magnetic field intensity will increase after increasing the current of an electromagnet? 19. What signifies value of the susceptibility in your experiment? 33 P a g e

34 Expt. No: Date: EXPERIMENT 9 TO DETERMINE THE DISPERSIVE POWER OF A MATERIAL OF PRISM USING SPECTROMETER AIM: To determine the dispersive power of a material of prism using Spectrometer. 1.2 APPRATUS: S. No Equipment Range Type Quantity 1 Spectrometer - Standard 1 2 Mercury vapor lamp 60 watts Standard 1 3 flint glass prism - Standard 1 4 reading lens - Standard FORMULA: PRINCIPLE: Refractive Index (µ): It is defined as velocity of light in vaccum µ = velocity of light in air Where A D sin m sin i 2 And sin r A sin 2 A Angle of Prism Dm Angle of minimum deviation the dispersive power of the material of the prism is given by b g av 2 Where b = the refractive index of the blue rays g= the refractive index of the green rays. 1.4 PRELIMINARY ADJUSTMENTS: The essential parts of spectrometer are b g w 1 av Where a) The telescope b) The collimator c) The prism table The following adjustments are to be made before the commencement of an experiment with a spectrometer. 34 P a g e

35 a) Eyepiece adjustment: the telescope is turned towards a bright object, say a white wall about 2 to 3 meter distance way and eyepiece is adjusted so that the cross wires are very clearly seen. OBSERVATIONS: Least count of the spectrometer (L.C) = 1 m.s.d No.of v.s.d = 301 / 30 = 1 1. Angle of prism (A) = 60 0 b) Telescope adjustment: Focus the telescope towards a distant (infinity) object. Focusing is done by changing the separation between the objective and the eyepiece of the telescope. Test for the absence of parallax between the image of the distant object and vertical cross wire. Parallax effect exists, if the cross wire and distant object are not at the same distance from your eyes. Now the telescope is adjusted for receiving parallel rays. Henceforth do not disturb the telescope focusing adjustment. c) Collimator adjustment: The slit of the collimator is illuminated with white light. The telescope is turned to view the image of slit and the collimator screw is adjusted such that clear image of the slit is obtained without parallax in the plane of the cross wires. The slit of the collimator is adjusted to be vertical and narrow. 1.5 PROCEDURE: a) Adjusting the prism to minimum deviation position: 1) The prism is placed on the prism table with the ground surface of the prism on to left or right of the collimator. The ground face of the prism does not face either collimator or telescope. 2) The ray of light passing through the collimator strikes the polished surface of the prism and undergoes deviation and emerges out through opposite polished surface as shown in figure. The deviated ray is seen through the telescope in position T2. 3) Looking at the spectrum the spectrum, the table is now rotated to one side, so that the spectrum moves towards undeviated path of the beam. The deviated ray also moves towards same side for some time and then starts turning back even if the prism table is moved in the same direction. The point at which the ray starts turning back is called the minimum deviation position. b) Finding angle of minimum deviation: 1) In the limiting position of spectrum, the deviation of the beam is minimum the telescope is fixed on the blue color and the tangent screw is slowly operated until the point of intersection of cross wire is exactly on the image. The readings for the blue color is noted in vernier-i and vernier-ii and tabulated in tabular form. 2) The telescope is now moved on to the red color, without disturbing the prism and again readings on vernier-1 and vernier-ii are noted and tabulated in table 3) Now the telescope is released and the prism is removed from the prism table. The telescope is now focused on to the direct ray and readings in vernier-i and vernier-ii are noted and tabulated. 35 P a g e

36 4) The difference of the readings between the deviated reading for blue color and the direct reading gives the angle of minimum deviation for blue color (DB). Similarly the difference of the readings between the deviated reading for red color and direct reading gives angle of minimum deviation for red color (Dr). 5) The refractive indices for blue and red rays are calculated using equations (II) and (III), (assuming angle of prism, A= 60 0 ). The values of µb and µr are substituted in equation (I) and the dispersive power of material of the prism is calculated. Fig 1: spectrometer 36 P a g e

37 1.6 OBSERVATIONS: Direct Reading: Left (VL) = Right (VR) =.. S.no Colours Readings in minimum deviation position MSR Left VSC TR (V1) MSR Right VSC TR (V2) Angle of minimum deviation (Dm) Aver V1~VL V2~VR age (Dm) Refractive Index ( µ ) 1.7 PRECAUTIONS: 1. The telescope and collimator should be individually set for parallel rays. 2. Slit should be as narrow as possible. 3. While taking observations, the telescope and prism table should be clamped with the help of Clamping screws. 4. Both vernier should be read. 5. The prism should be properly placed on the prism table for the measurement of angle of the Prism as well as for the angle of minimum deviation 1.8 RESULT : Dispersive power of material of the given prism (ω) = VIVA-VOCE QUESTIONS 1. What is spectrometer? 2. Define refractive index. 3. Define dispersive power of a prism. 4. How does refractive index change with wave length? 5. Does the deviation depend on the angle of prism? 6. What is prism? 7. Which colour in the spectrum is having maximum and minimum refractive index? 8. What is Refractive index? 9. What is the function of Collimator? 10. What do you mean by Angle of Prism? 11. What is Dispersion of Light? 12. What is the main optical action of the prism? 13. What type of material prism is used in this experiment? 37 P a g e

38 Expt. No: Date: EXPERIMENT 10 TO DETERMINE THE MAGNETIC INDUCTION AT VARIOUS POINTS ON THE AXIS OF A CURRENT CARRYING CIRCULAR COIL, USING STEWART AND GEE S TYPE OF GALVANOMETER. 1.1 AIM: To determine the magnetic induction at various points on the axis of a current carrying circular coil, using Stewart and Gee s type of galvanometer. 1.2 APPARATUS: S. No Equipment Range Type Quantity 1 Stewart and gee s galvanometer - Standard 1 2 DC power supply 60 watts Standard 1 3 ammeter plug key - Standard 1 4 commutator - Standard 1 5 rheostart and connecting wires. Stewart and gee s galvanometer, DC power supply, ammeter plug key, commutator, rheostat and connecting wires. 1.3THEORY: Imagine a circular coil of radius (a) meter, carrying (i) ampere current. Let (n) be the number of turns in the coil. Then the magnetic induction at a point(x) meter away from the coil, is given by B= μ 0nia 2 2(x 2 +a 2 ) 3 2 Also we have tangent law in magnetism. Let BH and B be the earth s and applied magnetic fields which are perpendicular to each other. A freely suspended needle in these fields comes to rest in a direction shown in figure. If the needle makes an angle (θ) with direction of BH, then Tan θ = B B H B = BH tan θ 1.4 PROCEDURE: 1) Stewart and Gees apparatus is so oriented that the circular coil is in magnetic meridian of the magnetic needle. That means keeping the magnetometer platform exactly at O of the scale, orient the Stewart and Gee s apparatus in such away that the magnetic needle is exactly below the circular coil and parallel to it. 2) Set the aluminum pointer to 0 0 position. 3) Now connect the circuit as shown in figure. 4) Set the voltage to 6 or 8 V Dc so that the deflection at the centre position in the magnetometer does not cross P a g e

39 Tan θ S.no. 5) Initially if the keys were inserted in the gaps (1) and (2), then change them to the gaps (3) and (4). Now the direction of current is changed, obviously deflection also get changed. However the magnitude of deflection should be same. If deflection is different, then the coil is not exactly in the magnetic meridian. So turn off the circuit and readjust the orientation. 6 Keeping the keys in the gaps (1) and (2) note the deflections (θ1) and (θ2) of the magnetic needle. Then inserting the keys in the gaps (3) and (4) note down (θ3) and (θ4). 7 Now move the platform to the 2 cm away from the centre either towards east or towards west. Repeat step (6). 8 Keeping the keys in the gaps (1) and (2) note the deflections (θ1) and (θ2) of the magnetic needle. Then inserting the keys in the gaps (3) and (4) note down (θ3) and (θ4). 9 Now move the platform to the 2 cm away from the centre either towards east or towards west. Repeat step (6). 10 Increasing the distance of platform from the coil, in steps of 2 cm, repeat step (6), till the deflection is Initially if the platform is moved towards east, then brought it back and move towards west. Repeat the experiment in same manner. Deflections are entered in to the tabular form. 1.5 MODEL GRAPH: Plot the graph, as shown in figure. (A) and (B) are called inflection points. The magnetic field of induction is maximum at the centre and decreases quite rapidly as we move away from the centre. It reaches a constant value at the points (A) and (B). The distance between (A) and (B) is found to be equal to the radius of the coil (a). TABLE: Distance between the deflection magnetomete r and center of coil. (x) m Deflection in the magnetometer when moved towards East West B=BHtan θ B= μ 0nia 2 2(x 2 +a 2 ) 3 2 Θ 1 Θ2 Θ3 Θ4 Mea n ΘE tan θe Θ1 Θ2 Θ3 Θ4 Mea n Θw Tan θw θ E + θ W 2 39 P a g e

40 1.6 PRECAUTIONS: 1) Once the coil is set in the magnetic meridian of the magnetic needle it should not be disturbed. 2) Rheostat and ammeter should be kept at a distance from Stewart and Gee s apparatus, otherwise they would influence the magnetic needle. 3) The deflections must be in between 60 and 30. 4) While shifting the flat form towards east or west, the Stewart and Gee s apparatus should be firmly held, so that the coil does not get disturbed from the magnetic meridian of the needle 1.7 RESULT: Magnetic induction at several points on the axis of current carrying circular coil is determined by using Stewart and Gee s type tangent galvanometer. 1.9 VIVA-VOCE QUESTIONS 1) What is the magnetic induction formula at a point x, away from the center of the circular coil? 2) What will be the Magnetic field value at the center of a current carrying coil? 3) Does earth s horizontal magnetic field value remain same everywhere or it fluctuates? 4)What are the two factors to calculate the earth s horizontal magnetic field value online. 5) The angle which you measure by the Deflection Magnetometer is with reference to the earth s magnetic field component or the magnetic field produced by current carrying coil? 6) Why do you put apparatus (Wooden Frame along with circular coil) in East-West Direction? 7) What is commutator and what its role in experiment? 8) What is he difference between Helmholtz coil and Solenoidal? 9) What is the relation between Gauss and Tesla? 10)What is the unit of magnetic field intensity H? 11)When you plot the graph in between the tan theta and distance, you observe Gaussian type shape of the curve. On this curve you find the points of inflection what is the formula for that? 12)The magnetic field of induction increases one side of the center and decreases on other sides. Can we create the uniform magnetic field with the help of this concept? 40 P a g e