Roll No:. Branch:. Academic Year:

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2 SIDDARTHA INSTITUTE OF SCIENCE & TECHNOLOGY (Approved by A.I.C.T.E., New Delhi & Affilliated to J.N.T.U.A, Ananthapuramu) Siddharth Nagar, Narayanavanam Road, Puttur Chittoor Dist.,A.P., INDIA Name: Roll No:. Branch:. Academic Year:

3 College Vision To be one among the premier institutions of the country in producing ethically strong and technically sound engineers and managers to serve the nation. College Mission To create sacred environment for the students to acquire knowledge through innovative and professional approach and utilize it for the welfare of the mankind.

4 BS&H Department Mission The Department of Basic Sciences & Humanities aims to nurture, excite and fertile young minds by strengthening leadership qualities and inspiring research environment to achieve all round excellence which would extend the frontiers of knowledge and contribute significantly in nation building. BS&H Department Vision To generate high quality human knowledge and its resources in our core areas of competence and in emerging challenges to make valuable contribution in technology for Social and Economic development of the nation. To proivide students with soft skills and behavioural training programmes in order to develop their over all personality and social consciousness. To provide a strong support in science and technology where students and staff collaboratively to build their career goals, equipped well with knowledge and skills to lead life to cohesion and harmony adopting high values on the society.

5 ENGINEERING PHYSICS LAB DO S 1. Always answer questions in complete sentences unless the question is only a numerical calculation. 2. Always include units when mentioning a numerical result in a sentence. 3. Read all steps in the lab procedure so you do not miss out on data you need to complete your lab report. 4. Draw your graph neatly and set up the axes so that the plot takes up most of the piece of graph paper and spreads out your data points. Unless instructed, your graph does not need to include the origin (0,0). 5. Make sure the divisions on the axes of your plots are evenly spaced. 6. Put a title (in words) at the top that describes what is in graph. 7. Label your plot axes with a word description, symbol, and units in parenthesis. Example: Force, F (N) 8. Draw a small box or circle around each point used to calculate the slope of the line. Choose two easy to read points that are on the line and are not data points.

6 DON TS 1. Never write your summary on your lab/data sheet - use lined paper or type it. 2. Do not simply say human error as a reason for not getting an expected result it tells your audience nothing. Be specific (e.g., delay due to reaction time in operating a stop watch). 3. Do NOT say your results are close or agree with the expected if they do not (i.e., and 23 are NOT pretty close!). When your results are way off (or not what you expected) ASK THE INSTRUCTOR or you may lose points on your lab report. 4. Do not draw more than one graph or plot per sheet of graph paper. This means you do not draw another graph on the back side of the piece of paper either. 5. Do NOT mix units in a graph or they won t cancel properly in the slope. Use the same unit for the same type of number on both axes (e.g., use N (= kg m/s 2 ) and m/s 2 NOT N and cm/s Do not connect the dots when drawing a line (straight or curved) to your data, unless instructed to do so. 7. Never use data points to calculate the slope of a line or the y-intercept. 8. Do not measure the y-intercept off of your graph if your graph does not include the origin (0,0). Use the equation of a line (y = mx + b) to solve for the y-intercept algebraically.

7 LIST OF EXPERIMENTS S.No. Name of The Experiment Page. No. 1 Diffraction grating - Normal Incidence method 1 2 Dispersive Power of the Prism Spectrometer 5 3 Newton s Rings Determination of thickness of a thin object by optical method (parallel fringes) Magnetic field along the axis of a current carrying coil- Stewart and Gee s method B-H Curve 19 7 Determination of Numerical aperture and acceptance of an optical fiber 23 8 Energy gap of a material using p-n junction diode Particle size determination laser 31 Lasers diffraction due to a single slit 33 Lasers diffraction due to a double slit Determination of wavelength of laser by diffraction grating 41

8 INDEX S. No. Date Name of The Experiment Marks Initials

9 DIFFRACTION GRATING NORMAL INCIDENCE METHOD Exp No :: Date :: AIM : To determine of wavelengths of various colours of Mercury Spectrum using Diffraction grating in Normal Incidence method APPARATUS : FORMULA : Plane diffraction grating, spectrometer, Mercury light, reading lens. Normal Incidence method : The wavelength can be calculated by normal incidence method is λ = sin o nn (1) Where λ = wavelength in Å θ = Angle of diffraction in degree n = Order of the spectrum N = No.of lines per cm PROCEDURE : Normal Incidence method : 1. Preliminary adjustments of the spectrometer are made, focusing and adjusting the eye piece of the telescope to a distant object. 2. The grating table is to be leveled with a spirit level. 3. The grating is mounted on the grating table for the normal incidence. 4. The slit of the collimator is illuminated with Mercury light. 5. The direct reading is taken; the telescope is turned from this position through 90 o and fixed in this position as shown in figure1. 6. The grating is mounted vertically on the grating platform, the rulings on it being parallel to the slit in the collimator. 7. The platform is now rotated until the image of the slit as reflected by the glass surface is seen in the telescope. The vertical cross wire is made to coincide with the fixed edge of the image and the platform is fixed in this position. 8. The vernier table is now rotated in the appropriate direction through 45 o, so that the rays of light from the collimator fall normally on the grating.

10 DIAGRAM : OBSERVATIONS : Number of lines (as marked on the grating) per inch = Number of lines per cm N = TABLE :: Determination of wavelength of different colours Readings on the Order of circular scale when the Colour Direct reading (deg) telescope is on the spectrum Right hand side (deg) Difference (deg) λ Vernier I Vernier II Vernier I Vernier II θ 1 θ 2 Mean θ sin θ (A 0 )

11 9. The telescope is now released and rotated it so as to catch the first order diffracted image on one side say right (or left). Knowing θ, n and N, the wavelength (λ) of the given source of radiation is calculated using equation (1) 10. The Telescope is now released and rotated it so as to catch the first order diffracted image on one side, say right (or left). With mercury light, images of the slit with different colours, very close to each other are seen. Then the point of intersection of the cross wires are to set on the red colour in the first order spectrum which is left to the normal white slit. The readings of the vernier-i and vernier-ii are noted down. 11. Similarly, the readings of the other colours are also to be noted down. Now the telescope is focused to the direct ray passing through the grating and the point of intersections of the crosswire is set on the direct way. The reading in the vernier-i and vernier-ii are noted. The difference in the readings corresponding to any one gives the angle of diffraction θ for that line in the first order spectrum. RESULT : The wavelength (λ) of different colours of the given light radiation using diffraction grating in normal incidence method is determined.

12 DIAGRAM:

13 DISPERSION OF LIGHT (PRISM SPECTROMETER METHOD) Exp No :: Date :: AIM : To determine the dispersive power of the material of the given prism. APPARATUS : Spectrometer, mercury vapour lamp, crown glass prism, reading lens. FORMULA : The refractive index of the material of the prism is given by: μ = A D sin 2 A sin ( 1 ) Where A = the angle of the equilateral prism in deg D = the angle of minimum deviation in deg The dispersive power (ω) of the material of the prism is given by: B R (2) Where µ B = the refractive index of the blue ray μ R = the refractive index of the red ray B μ = R 2

14 OBSERVATIONS : Least count of the vernier of the spectrometer = Angle of the prism (A) = 60 0 Direct ray Reading Vernier I =... Vernier II =... TABLE :: Determination of Refractive index of different colours Angle of minimum S.No Colour of the line Reading corresponding to minimum deviation position (deg) deviation = (direct reading) (reading of the minimum deviation position) (deg) D = V 1 + V 2 2 (deg) μ = A D sin 2 A sin 2 Vernier I Vernier II Vernier I Vernier II CALCULATION :

15 PROCEDURE : 1. The prism is placed on the prism table with the ground surface of the prism on to the left or right side of the collimator. 2. Vernier table is then fixed with the help of the vernier screw. 3. The ray of light passing through the collimator strikes the polished surface BC of the prism at Q and undergoes deviation along QR and emerges out of the prism from the face AC. Then the deviated ray (continuous spectrum) is seen through the telescope in position T Looking at the spectrum the prism table is now slowly moved on to one side, so that the spectrum moves towards undeviated path of the beam. 5. The deviated ray (spectrum) also moves on to the same side for some time and then the ray starts turning back even though the prim table is moved in the same direction. 6. The point at which the ray starts turning back is called the minimum deviation position. 7. The telescope is now fixed on the blue colour and the tangent screw is slowly operated until the point of intersection of the crosswire is exactly on the image. 8. The reading for the blue colour is noted in vernier I and vernier II and tabulated in table. This reading is called the minimum deviation reading for the blue colour. 9. The telescope is now moved on to the red colour, without disturbing the prism table and again the readings on vernier I and vernier II are noted and tabulated in table. 10. Next the telescope is released and the prism is removed from the prism table. 11. The telescope is now focused on to the direct ray and the reading in vernier I and vernier II are noted and tabulated in table. 12. The difference of the readings between the deviated reading for the blue colour and the direct reading gives the angle of minimum deviation reading for the blue color (D B ). 13. Similarly the difference of readings between the deviated reading for the red colour and the direct reading gives the angle of minimum deviation reading for the red color (D R ). 14. The refractive indices for the blue and red rays are calculated using equation (1) (assuming the angle of prism 60 0 ). 15. The values of μ B and μ R are substituted in equation (2) and the dispersive power of the material of the prism is calculated. PRECAUTIONS : 1. Don t touch the polished surface of the prism with hands to avoid finger frints. 2. Use reading lens with light while taking the readings in vernier scale. 3. The mercury light should be placed inside a wooden box. RESULT : The dispersive power (ω) of the material of the given prism is

16 DIAGRAM : MODEL GRAPH : Y D n 2 D m 2 Number of rings m n X

17 NEWTON S RINGS Exp No :: Date :: AIM : rings. To determine the radius of curvature of the surface of the lens by forming Newton s APPARATUS : Travelling microscope, sodium vapour lamp, plano convex lens of about 100 cm focal length, another convex lens of about 15 to 20 cm focal length, a thick glass plate, a magnifying glass, a black paper. FORMULA : The radius of curvature of the surface of the lens by forming Newton s rings can be calculated by R 2 2 Dn Dm cm 4 n m (1) Where R = radius of curvature of the surface of the lens in contact with the glass plate (P 1 ) in cm D n = diameter of n th ring in cm D m = diameter of m th ring in cm λ = Wavelength of the light radiation in cm PROCEDURE : 1. The point of intersection of the cross wire in the microscope is brought to the center of the ring system with one of the cross wires is perpendicular to the line of travel of the microscope. 2. The wire must be set tangential to any one ring and starting from the center of the ring system, the microscope is moved to one side, say left, across the field of view counting the number of rings. 3. After passing beyond 25 th ring, the direction of motion of the microscope is reversed and the cross wire is set at the 20 th dark ring, tangential to it. 4. The reading on the microscope scale is noted using a magnifying lens. 5. Similarly, the readings with the cross wires set on 35 th, 30th, 25 th, nd dark ring are noted. 6. The microscope is moved in the same direction and the readings corresponding to the 5 nd, 10th, 15 th, th dark ring on the right side are noted. 7. Readings are to be taken with the microscope moving in and the same direction to avoid errors due to backlash. 8. The observations are recorded in the table.

18 OBSERVATIONS : Wavelength of the light radiation λ = 5893 A o TABLE :: Determination of radius of curvature of the lens Microscope Reading Diameter of ring No. of (cm) rings (L 1 - R 1 ) Left side L 1 Right side R 1 (cm) Square of diameter of the ring (cm 2 ) Radius of curvature of the lens (R) (cm) CALCULATION :

19 9. A graph is drawn with the number of rings as abscissa (X- axis) and the square of diameter of the ring as ordinate (Y- axis). 10. The nature of the graph will be a straight line as shown in figure From the graph, the values of D n 2 and D m 2 corresponding to two numbers n and m are noted. 12. Using these values in equation (1) the radius of curvature of the lens is calculated. PRECAUTIONS : 1. Wipe the lens and glass plates with cloth before starting the experiment. 2. The center of the ring must be dark. 3. Use reading lens with light while observing the readings 4. Before starting the experiment make sure that movement of microscope in both sides (left and right side) of the rings. RESULT : cm. The radius of curvature of the surface of the lens by forming Newton s rings is

20 DIAGRAM : OBSERVATIONS: Length of the wedge L = Wavelength of the source of light λ = TABLE :: Determination of fringe width S.No Fringe number Microscope reading (a) cm Width of 5 fringes (a - b) = c cm Fringe width β = c / 5 cm Average β = CALCULATION :

21 DETERMINATION OF THICKNESS OF A THIN OBJECT BY OPTICAL METHOD (PARALLEL FRINGES) Exp No :: Date :: AIM : To determine the diameter or thickness of a thin wire by interference method. APPARATUS : Thin wire, two optically plane glass plates of 1 x 3, traveling microscope, sodium lamp, reflecting glass plate, magnifying glass. FORMULA : The diameter of a thin wire by interference method can be calculated by d L cm 2 Where d = diameter or thickness of a wire in cm λ = wavelength of source of light in Å L = length of the wedge in cm β = fringe width in cm PROCEDURE: 1. The eye piece of the microscope is adjusted as shown in the figure, so that the fringes are clearly seen. 2. The microscope is moved to one end of the glass plate until the cross wire coincides with one of the fringes, say n th fringe and the microscope reading is noted. 3. The microscope is now moved to ( n + 5 ) th fringe and the reading noted. 4. The microscope is moved in the same direction and the reading is noted each time at ( n + 1) th, ( n + 15) th.. ( n + 40 ) th fringe. 5. The observations are tabulated in the table. PRECAUTIONS : 1. The microscope should move in one direction from left to right or right to left, so the back error is avoided. 2. To achieve good accuracy in the measurement of l should be repeated twice or thrice. RESULT : The diameter or thickness of a thin wire by interference method is cm.

22 DIAGRAM : MODEL GRAPH :

23 MAGNETIC FIELD ALONG THE AXIS OF A CURENT CARRYING COIL (STEWRT & GEE S METHOD) Exp No :: Date :: AIM : To determine the field of induction at several points on the axis of a circular coil carrying current using Stewart & Gee s type of tangent galvanometer. APPARATUS : Stewart and Gee s galvanometer, Battery eliminator, Ammeter, Commutator, Rheostat, Plug Keys, Scale, connecting wires. FORMULA : The magnetic field can be calculated by B onia 2 2 x a Tesla Where μ 0 = permeability of free space = 4π x 10-7 Henry / m i = current through the coil in Amp a = radius of the coil in m n = number of turns in the coil x = distance of the point (P) from the centre of the coil in m PROCEDURE: 1. With the help of the deflection magnetometer and a chalk, a long line of about one meter is drawn on the working table to represent the magnetic meridian and another line perpendicular to this line is also drawn. 2. The Stewart & Gee s galvanometer is set with its coil in the magnetic meridian as shown in the figure The external circuit is connected as shown in figure 1, keeping the ammeter, rheostat away from the deflection magnetometer. 4. Magnetometer is set at the centre of the coil and rotated to make the aluminum pointer read (0,0) in the magnetometer. 5. The key K is closed and the rheostat is adjusted so as the deflection in the magnetometer is about The current in the commutator is reversed and the deflection in the magnetometer is observed. The deflection in the magnetometer before and after reversal of current should not differ much.

24 θ =( θe+ θw)/2 Tanθ B= Be Tanθ OBSERVATIONS: Current through the coil = i =. Amp. Number of turns in the coil = n = Radius of the coil = a =.. cm B e = 0.38 x 10-4 Tesla = 4π x 10-7 Henry / m μ 0 TABLE:: Determination of magnetic field S. N o Distance of deflection magnetom eter from the centre of the coil (x) (cm) Deflection in the magnetometer East side θ 1 θ 2 θ 3 θ 4 Mean θe Tan θe Deflection in the magnetometer West side θ 1 θ 2 θ 3 θ 4 Mean θw Tan θw onia B 2 2 x a Tesla

25 7. The deflections before and after reversal of current are noted when d = 0 and the readings are noted in the table. 8. The magnetometer is moved towards East along the axis of the coil in steps of 2cm at a time. 9. At each position, the key is closed and the deflections before and after reversal of current are noted and the mean deflection be denoted as θ E. 10. The magnetometer is further moved towards east in steps of 2cm each time and the deflections before and after reversal of current are noted until the deflection falls to The experiment is repeated by shifting the magnetometer towards west from the centre of the coil in steps of 2 cm, each time and deflections are noted before and after reversal of current. The mean deflection is denoted as θ W. 12. A graph is drawn between x (the distance of the deflection magnetometer from the center of the coil) along X- axis and the corresponding Tan θ E and Tan θ W along Y- axis. The shape of the curve is shown in figure2. PRECAUTIONS: 1. The ammeter should keep away from deflection magnetometer. 2. The deflection in the magnetometer should not exceed more than 60. RESULT : The field of induction at several points on the axis of a circular coil carrying current is determined using Stewart & Gee s type of tangent galvanometer.

26 DIAGRAM : OBSERVATIONS : S.No Resistance Ώ CH 1 V/s CH 2 V/s S V V/s S H V/s Area of loop Energy loss

27 B.H. CURVE Exp No :: Date :: AIM : To trace the hysteresis curve of a transformer core using a CRO and find the energy loss per unit volume per cycle and corecivity and retentivity of the material of the core. APPARATUS : Given transformer core with Primary (Np) and secondary (Ns) windings a step down transformer (Tr) having an output 6V. Low loss capacitor Cs, Resistors R and R 1 and AC mains supply (220v-50 Hz) and CRO. FORMULA : The energy loss can be calculated by (E. L) = N 1 N 2 R R 1 C AL S V S H area of the loop in joules cycle /unitvolume Where N 1 = No. of turns of primary coil = 200 turns N 2 = No. of turns of secondary coil = 400 turns R 1 = Resistance between terminals R 1 = 5, R 2 = 22, R 3 = 45 ohms R = 1K ohms C = 4.7 μf L = Length of specimen = cm A = Area of cross section of transformer specimen = 2.54 cm 2 PROCEDURE: The phenomenon by which the magnetic induction (B) lags behind the magnetizing field (H) is called hysteresis. 1. The hysteresis curve-graph with H on axis & corresponding B (of the material) will be as shown in fig The area under the B-H curve gives the hysteresis loss per cycle that is the work done per unit volume per cycle. OQ gives the value of the retentivity (Br) that is the remanent induction even when the field H is removed. OR gives the value of the coercivity (Hc) that is the negative field to be applied to demagnetize the specimen completely. 3. The circuit diagram required for experiment is as shown in fig.2.connect the primary terminals of the specimen to PRIMARY and secondary to SECONDARY terminals. Adjust the CRO to work on external mode (the time base in switched off) Connect terminal Vertical CRO to the vertical input of the CRO.

28 CALCULATION :

29 4. Connect terminal HORIZONTAL CRO to the horizontal input of the CRO. Switch ON the power supply of the unit. The hysteresis loop is formed. Adjust the horizontal and vertical gains such that the loop occupies maximum area on the screen of the CRO. Once this adjustment is made don t disturb the gain controls. The position of horizontal gain knob will give horizontal sensitivity SH (Volts/m). Similarly the position of vertical gain knob will give vertical sensitivity Sv (Volts/m). 5. Trace the loop on a translucent sheet (butter paper) and reproduce the same on graph paper. Estimate the area of the loop is sq. Meter. 6. The energy loss is given by (E. L) = N 1 R C N 2 R 1 AL S V SH area of the loop in joules cycle /unitvolume RESULT : The energy loss of B-H loop is

30 DIAGRAM : CONNECTOR Optical Fiber Kit OPTICAL FIBER NA Jig with gratical plate TABLE :: Determination of acceptance angle and numerical aperture S.No L in mm W in mm N.A= W 2 2 ( 4L W ) 1 2 max in deg Avg NA = Avg max =

31 NUMERICAL APERTURE AND ACCEPTANCE ANGLE OF AN OPTICAL FIBER Exp No :: Date :: AIM : To determine the numerical aperture and acceptance angle of the given optical fiber cable. APPARATUS : FORMULA : Fiber optics light source, NA Jig, one meter optical fiber cable, gratical plate. The numerical aperture of an optical fibre can be calculated by PRINCIPLE : N.A = sin Where W = Diameter of the spot in mm L = Distance of the gratical plate from SMA in mm Numerical aperture is a measure of how much light can be collected by the optical system. It is the product of refractive index of the incident medium and sine of the maximum ray angle. i.e., N.A = n i sin max where n i =1 for air. Hence N.A = sin max For step-index fiber as in the present case, the N.A is 2 2 N.A = ( n ) core n cladding For very small differences in refractive indices, the equation reduces as follows max (4L 2 W W 2 ) 1 2 N.A = n core 2 Where is the fractional difference in refractive index

32 CALCULATION :

33 PROCEDURE : 1. Collect one end of the SMA optical fiber cable to optical light source at the SMA termination and other end to the NA Jig as shown in the figure. 2. Keep the movable gratical plate at approximately 1cm or 10mm. 3. Keep the intensity control at maximum level. 4. Switch on the light source and red spot of approximately 4 mm diameter appears on the gratical plate consisting of concentric circles of known diameters. Dark ring will facilitate good contrast. 5. Bring the gratical plate close towards SMA connector and correct the center spot by eye adjustment if necessary. 6. Position the gratical plate so that the diameter (W) of the red spot is made exactly equal to the concentric one of the circle. 7. Now measure the distance (L) of the gratical plate from SMA connector on the scale provided. 8. The diameter (W) of the red spot can be varied by varying the length (L). Repeat the same for different concentric circles by varying the length (L) and tabulate the readings. W 9. Compute N.A from the formula N.A = PRECAUTIONS : sin 1. Any circumstances do not look directly into the LASER beam. 2. Do not shine reflected laser light toward anyone. 3. It is very important that the optical source should be properly aligned with the cable. 4. The distance from the launched point and cable is properly selected to ensure that the maximum amount of optical power is transferred to the cable. RESULT : Numerical aperture of the optical fiber = Acceptance angle of the optical fiber = max (4L 2 W 2 ) 1 2

34 DIAGRAM : Model Graph : Slope ln s

35 ENERGY BAND GAP OF A SEMICONDUCTOR Exp No :: Date :: AIM : To determine the energy band gap of a semiconductor. APPARATUS : Energy band gap of semiconductor trainer, tumbler flask, thermometer, connecting wires. FORMULA : The energy band gap of a semiconductor can be calculated by Energy gap E g = Slope X Boltzmann Constant ev where Boltzmann constant K = 1.38 X J/K PROCEDURE : 1. Switch on the Energy band gap of semiconductor trainer 2. Connect the supply provided on the trainer to the input voltage. 3. Connect the micro ammeter, which is provided on the trainer to the µa terminal. 4. Connect either of the diode, which is provided on the trainer. 5. Fix the diode to the cap of the tumbler flask. Provide two holes on the cap and insert a thermometer in one and a wire stirrer in the other. 6. Fill the tumbler flask with oil heated approximately C. Fix the cap and stir the oil well. This arrangement is good enough to maintain the temperature within ± C. 7. At any particular temperature, measure current as a function of the reverse bias voltage. This voltage can be obtained directly from the calibrations on the potentiometer. There is no need to use a separate voltmeter if a ten turn potentiometer (calibrated) is used. If the battery voltage is 1V, each turn corresponds to 150mV and each division on the scale corresponds to 1.5mV. 8. The biasing voltage is increased in steps and the corresponding current is noted. The constant current which is the saturation current which is the saturation current I S is noted from these observations at that temperature. 9. Open the cap of the flask and allow the temperature to decrease by 20 0 C, stir the liquid well, fix the cap and repeat the experiment for different temperatures by cooling the liquid in steps of 20 0 C. 10. Represent the results graphically.

36 T = t +273 K TABLE :: Determination of slope S.N o Increasi ng Temperature in o C Current in µa Decreasi ng Average t Increasi ng Decreasi ng Average I S 1/T x 10-3 K -1 ln I S CALCULATION :

37 11. Plot log 10 I S as a function of 1/T. Evaluate the slope and the forbidden energy gap of germanium. 12. Compare with the standard value. 13. Standard value of energy gap for germanium is 0.68 ev and for Silicon it is 1.1 ev. PRECAUTIONS : 1. The thermistor (water heater bath) and thermometer are kept at the same level in the oil bath. 2. The temperature of the thermistor should not be allowed to go beyond 80 o C RESULT : The energy band gap of the given semiconductor is ev.

38 DIAGRAM : TABLE :: 1:: Distance of screen from particle size d = cm Radius of the circle of n th S.No Order of the dark ring (n) order (r n cm) D = 1.22 λ n d r n cm Avg D = TABLE :: 2:: Distance of screen from particle size d = cm Radius of the circle of n th S.No Order of the dark ring (n) order (r n cm) D = 1.22 λ n d r n cm Avg D =

39 PARTICLE SIZE DETERMINATION LASER Exp No :: Date :: AIM : To determine the particle size ( lycopodium particles ) by using semiconductor Laser. APPARATUS : GaAs semiconductor laser, Lycopodium slides, screen, slide holder, optical bench, meter scale, etc. FORMULA : The particle size can calculated by using semiconductor laser is cm PROCEDURE : Where D is the size of the particle in cm λ is the wavelength of laser beam in cm d is the distance between the particle (slide) and the screen in cm n is the order of diffraction and r n is the radius of the circle in cm 1. Switch on the semiconductor laser and allow the laser beam to fall on the lycopodium slides which is placed on the optical bench. 2. Observe the diffraction pattern on the screen at its best. 3. Measure the diameter of the fringes of different orders. 4. By using the above formula, calculate the diameter of lycopodium particles. 5. Repeat the experiment by changing the position of the slide from the screen on the optical bench. PRECAUTIONS : 1. Don t see the laser beam directly. 2. Take the readings without parallax error. RESULT : The diameter of the particles is determined by using semiconductor laser and is found to be cm.

40 DIAGRAM : OBSERVATIONS : Width of the slit d = cm Distance between slit and screen D = cm TABLE : Determination of fringe difference Fringe reading in Travelling microscope Fringe S.NO number Right a cm Left b cm Difference of fringe readings x = a~b cm

41 LASERS DIFFRACTION DUE TO A SINGLE SLIT Exp No :: Date :: AIM : To determine the wavelength of given laser source by using diffraction pattern due to single slit. APPARATUS : FORMULA : Laser source, single slit, travelling microscope, thread, magnifying lens. The wavelength of given light source by using diffraction pattern can be calculated by PROCEDURE : where λ is wavelength of given light source in Å d is slit width in cm D is the distance between slit and screen in cm x n is the difference of fringes in cm n is the order of diffraction 1. The single slit is arranged in front of Laser source. 2. The laser beam is allowed to pass through it. Then we observe the diffraction pattern on the screen. D which is the distance between slit and screen can be measured by thread. 3. The diffraction pattern consists of central bright fringes followed by a few narrow fringes of varying intensity on either sides. 4. Here the distance from central fringe to first order on both side and similarly second, third, are measured by using travelling microscope. Thereby we can calculate difference or separation from table. 5. The width of the slit is measured with the help of travelling microscope. 6. The wavelength λ is calculated by using the above formula. PRECAUTIONS : 1. Take care about laser light and the slit is arranged in such a way that it must be rigid. 2. The distance D is between slit and screen is taken from centre of slit by using thread to minimize the error. 3. Take care about microscope readings while measuring the slit width. Å

42 CALCULATION :

43 RESULT : The wavelength of given laser source by using diffraction pattern due to single slit is determined and its value is Å.

44 DIAGRAM : OBSERVATIONS : Width of the slit d = cm Distance between slit and screen D = cm TABLE : Determination of fringe difference Fringe reading in Travelling microscope Fringe S.NO number Right a cm Left b cm Difference of fringe readings x = a~b cm

45 LASERS DIFFRACTION DUE TO A DOUBLE SLIT Exp No :: Date :: AIM : To determine the wavelength of given laser source by using diffraction pattern due to double slit. APPARATUS : FORMULA : Laser source, double slit, travelling microscope, thread, magnifying lens. The wavelength of given light source by using diffraction pattern can be calculated by PROCEDURE : where λ is wavelength of given light source in Å d is slit width in cm D is the distance between slit and screen in cm x n is the difference of fringes in cm n is the order of diffraction 1. The double slit is arranged in front of Laser source. The laser beam is allowed to pass through it. Then we observe the diffraction pattern on the screen. 2. These are interference bands produced by the two slits. Here the central maxima splits. We take the distance of separation from one end. 3. We measure consequently for next ten fringes separation, by using travelling microscope. 4. We get total separation between the fringes is 2 x n. 5. The width of the slit is measured with the help of travelling microscope. 6. The wavelength λ is calculated by using the above formula. PRECAUTIONS : 1. Take care about laser light and the slit is arranged in such a way that it must be rigid. 2. The distance D is between slit and screen is taken from centre of slit by using thread to minimize the error. 3. Take care about microscope readings while measuring the slit width. Å

46 CALCULATION :

47 RESULT : The wavelength of given laser source by using diffraction pattern due to double slit is determined and its value is Å.

48 DIAGRAM : TABLE : Determination of wavelength S.N o Order of diffraction, n The distance between grating and the screen, D (cm) Distance from central maximum (cm) On left, d 1 On right, d 2 Mean d sin θ = d d 2 + D 2 λ Å Avg λ=

49 DETERMINATION OF WAVELENGTH OF LASER BY DIFFRACTION GRATING Exp No :: Date :: AIM : To determine the wavelength of a given source of laser light using a plane transmission grating by normal incidence method. APPARATUS : Plane diffraction grating, laser source, meter scale, graph sheets and optical table. FORMULA : The wavelength of laser can be determined by, Å PROCEDURE : Where λ is wavelength of laser source in Å n is order of diffraction N is number of lines per inch on the grating Keep the grating in front of the laser beam such that the light is incident normally on it. When laser light falls on the grating, the diffraction pattern is produced on the screen in the form of bright spots which are called maxima. The central maximum along with other maxima which are formed on the screen. The positions of these bright spots can be recorded on the graph sheet (with the mention the order n) which is attached to the screen. The bright spot next to central maximum is called the first order maxima and the light next to the first order is second order maxima and so on. Each of the maxima corresponds to a specific diffraction angle θ which can be measured by applying trigonometry. The distance from central maxima to the first order on the left is to be noted as d 1 and the distance from central maxima to the first order on the right is to noted as d 2 is table. Repeated the experiment for higher orders of diffraction and tabulate the readings. Measure the distance between the grating and the screen and tabulate it as D. RESULT : The wavelength of laser beam, λ = Å

50