MUFFAKHAM JAH COLLEGE OF ENGINEERING AND TECHNOLOGY (SULTAN-UL-ULOOM EDUCATION SOCIETY) BANJARAHILLS, HYDERABAD-500034

MANUAL OF ENGINEERING PHYSICS PRACTICALS SEMESTER-I FOR B.E 1/IV 2016-17

Name

:

Hall Ticket No : Class

:

Section

:

LIST OF EXPERIMENTS NAME OF EXPERIMENT

PAGE NUMBER

1. POARIMENTER

1

2. DIFFRACTION GRATTING

4

3. SINGLE SLIT DIFFRACTION

8

4. NEWTON’S RINGS

11

5. LASER

14

6. OPTICAL FIBER

16

7. BIPRISM-WAVELENGTH

19

8. ULTRASONIC INTERFEROMETER

22

9. VERIFICATION OF MALUS LAW

26

MJCET

1. P O L A RI M E T E R AIM :

To determine the specific rotatory power of an optical active solution for example canesugar solution or glucose solution using a polarimeter

APPARATUS : Bi-quartz polarimeter, Mercury Vapour Lamp or white lamp, measuring jar, beaker, and physical balance, standard glucose solution.. FORMULA :

S = 10./ l.C

C = concentration of the solution , l = length of the solution in the polarimeter tube ,  is anlge of rotation of plane of

r

polarization , S = specific rotatary power

PROCEDURE : Take 10 gm sugar and dissolve it in 100

cc water (or glucose solution.) If necessary filter the solution. Illuminate mercury vapour lamp or an incandescent

bulb. Let the light be incident on the polariser. Look through

L

o

X

R

r

C

y

y b

b

the telescope at the other end and adjust it such that the field of view is well defined.

o

v

X

1

v

Figure

Take a clean polarimeter tube, fill it completely with distilled water and place it in position in the

polarimeter. Looking through the eyepiece and rotate the analyser and obtain the position of minimum

intiencity. Note the reading in the circular scale as 1. Empty the polarimeter tube and fill it completely with the given solution . Introduce the polarimeter tube in the polarimeter. Rotate the analyser and

again obtain the position of minimum intencity. Note the reading on the circular scale as 2. The difference between 1 and 2 gives the optical rotation  produced by the solution of concentration C. Repeat the experiment with solutions of other concentrations. OBSERVATIONS: Reading on the circular scale

for the position of minimum intencity

1 = ..........................

with distilled water in the tube

1

MJCET S. No.

Length of the tube (l)

Concentration of the solution C

Reading on Circular Scale for the position of tint of passage 2

Specific Optical rotatory Power rotation  = 1 2 S = 10./l.C

RESULT : The specific rotatory power of sugar / glucose is = .......................... degree.

( cm ) 2

gm

PRECAUTIONS : 1

There should not be air bubbles in the tube big enough to obstruct the path of light.

3

The Windows of the polarimeter tube should be clean. The caps of the tube should be screwed enough so that the solution does not leak out. They should not be screwed very tightly so that the window glasses are strained.

2

The concentration of the solution should be uniform.

2

MJCET SAMPLE VIVA QUESTIONS 1.

What is polarization of light.

3.

What are different types of polarized light.

2. 4. 5. 6. 7. 8. 9.

10.

What are different methods of producing polarized light. What is the optic axis in a crystal. What is optical rotation.

Why is plane polarized light rotated on passing through optically active substances. What are optically active substances.

Do all the substances rotate the plane of polarization in the same direction. On what factors does the rotation of plane of polarisation depends. What is specific rotatory power.

11.

On what factors the specific rotatory power depends.

13.

How does the specific rotatory power depend on temperature and wave length.

12. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.

What is the unit of specific rotatory power. What is a racemic mixture. What is nicol prism.

What is half shade plate.

Where it is placed in a polarimeter. What is a half wave plate.

What precautions you have to take while filling the tube. Why we use sodium lamp in this experiment.

What will happen if white light is used in the experiment. What is rotatory dispersion.

Give some example of optically active substances.

3

MJCET

2. DIFFRACTION GRATING BY NORMAL INCIDENCE METHOD AIM : To determine the wave lengths of spectral lines using diffraction grating. APPARATUS : Plane diffraction grating, spectrometer, spirit level, reading lens, source of light (mercury vapour lamp.) DESCRIPTION : A diffraction grating is a thin celluloid film containing nearly 15,000 lines per inch. This film is fixed between two optically plane glass plates. The celluloid film is obtained by evaporating a solution of cellulose acetate on original grating on a glass plate or specular metal. Hence it is also called replica transmission grating. PRINCIPLE : A diffraction grating has a number of parallel lines separated by equal distances. Each line is opaque to light while the space between them is transparent to light and acts as slit. Suppose ‘e’ is width of each slit and ‘d’ is the width of each opaque part. Then (e+d) is known as grating element. The reciprocal of grating elements is equal to the number of lines per cm. Suppose a beam of parallel rays is incident normally on the grating. The rays of different wave length (colours) undergo diffraction at different angles. For a particular wave length the principal maxima are obtained at angle given by : (e+d) Sin = n 1 N Sin = n or Sin = N n

or

Sin  Ao or cm nN Where ‘n’ is the order of maximum spectrum. The maximum number of orders available with a grating is given by nmax = 1/N  with the present grating we can observe two orders of spectra. or =

ADJUSTMENTS: Before performing the experiment the following adjustments are made: 1 2

Adjustment of spectrometer for parallel rays. Adjustment of grating for normal incidence.

ADJUSTMENT OF SPECTROMETER: The different parts of a spectrometer are arranged in the sequence, eye piece, telescope, collimator and prism table. EYE PIECE: Turn the telescope towards a white surface (say a wall). Looking through the eye piece move it in or out until the cross wires are clearly seen.

TELESCOPE: Turn the telescope towards a distant object out side the laboratory. Looking through the eye piece turn the pinion (adjustment wheel) until clear image of the object is seen at the cross wires without any parallax.

4

MJCET COLLIMATOR : Keep the spectrometer such that its collimator is facing a source of light. Illuminate the slit. Bring the telescope in line with the collimator. Adjust the distance of the slit from the lens of collimator by turning its adjustment wheel(pinion) until a clear image of the slit with sharp edges is obtained at the cross wires without any parallax. PRISM OR GRATING TABLE : Keep a spirit level on grating table parallel to the line joining two of the levelling screws and adjust them such that the bubble is at the centre. Now keep the spirit level in a perpendicular position and adjust the third screw to bring the bubble to the centre. ADJUSTMENT OF GRATING FOR NORMAL INCIDENCE : After adjusting the different parts of the spectrometer bring the telescope in striaght line with the collimator such that the vertical cross wire of eye piecec coincides with the light beam coming the slit (position straight T 1). Note the circular scale reading. Turn the telescope by exactly 900 and clamp it (position T2). Now it is at right angles to the collimator. Mount the grating vertically in its holder on the grating table. Release the vernier table and rotate it until the image of the slit is seen in the telescope by reflection from the grating (Fig - 1) ( If the image of the slit is not in view tilt the grating slightly by adjusting the levelling screws. Fix the vernier table and adjust its slow motion screws until the image of the slit coincides with the vertical cross wire. Note the reading on the circular scale. Release the vernier table and rotate it through exactly 450 (fig). Now release the telescope and bring it in line with the collimator. Turn the telescope to one side. At some angle spectral lines are seen. These lines should be centrally situated in the field of view. If the grating lines are not parallel to the slit the spectral lines will not be centrally situated.

Collimator

To bring them to centre we can either adjust the levelling screw or move one of the edges of the grating up or down.

C G

T2

 

T

T1

Left

Fig. 1

T Direct

Fig. 2

5

T

G

45 0 45 0

Right

MJCET PROCEDURE: After adjusting the grating in normal incidence position bring the telescope in straight line position with the collimator. Turn the telescope towards right hand side. At some angle we get

spectral lines. This is called first order spectrum. In the case of mercury vapour lamp violet, blue, green and yellow red lines are clearly seen. Adjust the telescope such that the vertical cross wire

coincides with the red line and note the readings in the circular scale. Next coincide the cross wire with

yellow, green, blue, violet lines in order and note the corresponding readings. Next turn the telescope to the left hand side and note the readings corresponding to lines violet, blue, green, yellow and red in

order. Half the difference in the readings corresponding to any one colour gives the angle of diffraction

( ) for that line in the first order spectrum. Calculate the wavelength of the line using S i n   o A or cm n.N

 =

Note down the number of lines marked on the grating and estimate number of lines N per cm. By using the formula. No. of lines per inch N= 2.54 OBSERVATIONS:

No. of lines per inch =

No. of lines per cm. N = Order of spectrum

Colour

Reading on circular scale

Vernier I

Left

Right

Difference in the readings of

Vernier II

Left

Ver - I

Right

2

Red

Yellow 1

Green Blue

Violet

6

Ver - II

2

Angle of Wavelength diffraction

Mean

2



=

Sin  n.N.

A or cm o

MJCET RESULTS : The wavelength of

Red line

=

------------------ Ao

Green line

=

------------------ Ao

Violet line

= ------------------ Ao

Yellow line

=

Blue line

=

------------------ Ao

------------------ Ao

PRECAUTIONS : 1. 2.

The grating must be handled carefully. It must be held by edges only. On no account the celluloid film be touched. The difference in the readings of vernier I and vernier II for any position should be 180 0.

SAMPLE VIVA QUESTIONS 1.

What is diffraction.

3.

Which undergoes more diffraction, light or sound.

2. 4. 5. 6. 7. 8. 9.

10.

What is difference between interference and diffraction. What is a diffraction grating.

What are different types of grating. What type of grating you are using.

Why the grating is placed between glass plates. What is grating element.

What do ‘e’ and ‘d’ represent.

If a grating has 10,000 lines per cm. What will be its grating element.

11.

How to convert no. of lines per inch into no.of lines per cm.

13.

What is meant by order of spectrum.

12. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.

If the above conversion is not done what will be the unit of wave length. On what factors the possible no. of orders of spectra depends. What is the formula. In the present grating how many orders you can expect. What is normal incidence method.

While the grating is at 45 0, we see many images of slit, Why? What is the formula in normal incidence method.

Can we use grating for minimum deviation position. If so what is respective equation. What is the difference in the spectra produced by a grating and a prism What is the cause of the above difference.

What is the difference in the first and second order spectra.

What is dispersive power of a grating. On what factors it depends. Why grating produces less intense spectrum than prism spectrum. 7

MJCET

3. SINGLE SLIT DIFFRACTION AIM : To determine the value of the wavelength  of given source of light by employing a single slit diffraction method

APPARATUS : Sodium Vapor lamp, Single slit of adjustable width and Spectrometer.

H

3               

        



                 3

PROCEDURE: Adjust the spectrometer as described in other experiments. Illuminate the slit of the collimator with sodium light. Mount the single slit on the prism table such that rays of light from the collimator are incident normally on the slit. Bring the telescope in line with the collimator so that the light from the collimator is received. Looking through the telescope narrow down the slit. A diffraction pattern is seen. The pattern consists of a central bright region flanked by much weaker maxima alternating with dark bands. Adjust the width of the slit such that the central band is sufficiently wide. Move the telescope to one side such that the cross wire is beyond the third dark band. Tighten the main screw of the telescope. Using the tangential procession screw move the telescope in the reverse direction and make the cross wire coincide with the third dark band. Note down the reading. Similarly note the readings of second and first order dark bands. Continue to move the telescope to the other side of the central band and note the readings of the corresponding dark bands on this side also. From these readings find the diffraction angles 1, 2, 3. for m = 1,2,3,…

8

MJCET Remove the slit carefully and measure the slit width ‘a’ using travelling microscope. Calculate ‘’ value using ‘  ’ for different minima.

Formula



a sin  m m

o

A or cm

Observations

Sl.

Number

No of the dark fringe(m)

Position of the telescope dark fringe pattern

Left (L)

V1 ( L )

V2 ( L )

2 m

Right (R)

V1 ( R )

V2 ( R )

V (L) 1

~ V1 (R) V2 (L) ~ V2 (R)

3 2 1

Least count of travelling microscope =

cm

Width of the slit (using travelling microscope) ‘a’ =

cm

RESULT: The wavelength of the given light  = .................. Ao

9

m

=

a sinm m

MJCET PRECAUTIONS: 1. 2.

Avoid backlash errors while taking the readings Adjust screw the width of the slit slowly till you observe at least three orders in the field of view of the telescope.

SAMPLE VIVA QUESTIONS :

1. 2. 3. 4. 5. 6.

What is diffraction? Distinguish between Fresnel and Fraunhoffer diffraction? Distinguish between diffraction and interference? Explain the formation of fringes using single slit diffraction? How do you get more resolution in diffraction pattern? If white light is used what kind of change you expect in the diffraction pattern?

10

MJCET

4. NEWTON’S RINGS

AIM : To determine the wavelength of sodium light by means of Newton’s Rings.

APPARATUS : Sodium lamp, condensing lens, plano convex lens of 100cm focal length, plane glass plate, travelling microscope and a thin optically flat glass plate. PRINCIPLE : Interference

FORMULA :

=

2

D

m

2

-D

n

4 R (m-n)

cm

where Dm and Dn be the diameters of the mth and nth dark rings respectively and R the radius of curvature of the lower face of the creating rings , then the wavelength of the light is given by the M

relation.

Plano Convex Lens

Glass Plate

C.L.

P2

So di um Lamp

P1

R= l /6h + h/2 Where l = average distnat between two legs of spherometer, 2

i.e (l +l +l )/3 , h = hight of the curve surface of the lens. 1

2

3

ADJUSTMENT : The microscope is made vertical. The eye piece is adjusted such that the cross wires are clearly seen. If necessary the cross wires are adjusted such that one of the wires is perpendicular to the direction of motion of the microscope. A mark is made on the table. The microscope is moved up or down such that the mark is seen clearly. A black paper(carbon paper) is placed on the table and a thin optically flat glass plate is placed on it. Light rays from a sodium vapour lamp are made to be incident normally on this plate with the help of a thin glass plate held at 45 0. Some of the rays incident on the horizontal plate get reflected from its upper surface. These rays pass through the inclined plate and enter the microscope. When seen through the microscope, we get a bright yellow field of view. A plano convex lens is placed on the horizontal plate such that its centre is exactly below the microscope. A number of concentric dark and bright circles are seen. The microscope is finally adjusted such that the rings are clearly seen. The central spot should be dark. If the central spot is bright the lens is cleaned or it is tapped slightly. The experimental setup is shown in the diagram. PROCEDURE : The setup is adjusted such that the intersection of the cross wires is at the centre of the central spot. The microscope is moved towards left, counting the number of rings, say upto 11 rings. There after moving back the microscope the cross wire is set tangentially to the 10 ring. The reading on the horizontal scale and the 11

MJCET vernier coincidence are accurately noted. The reading of the 6th, 5th,4th,3th 2nd and 1st rings are noted. The microscope is thereafter moved in the same direction till 1st ring is reached on the right side and thus the readings are recorded. Thereafter the readings are noted for 1th, 2nd,............. upto 10th ring. The readings are noted in table 1. The diameters of different rings are noted from the differences between the corresponding readings on the right and the left side. The difference in the squares of the diameters of the rings is found. you will find all the values to be almost constant (table2) . The lens is removed and the radius of curvature ‘R’ of the surface in contact with the plane glass plate is accurately measured using a spherometer. The wavelength of the light can be calculated using. m

-D

2

n

4 R (m-n)

A graph is plotted between the number of the rings and square of its diameter. A straight line graph is obtained. Its slope is found out. The wavelength of the light can be calculated from

=

(Diameter)2

 =

2

D

Slope

No. of ring

4R

OBSERVATIONS : Least count of the travelling microscope = ................................... Number of Sl. No. Rings 10

Microscope Readings

On left side

On right side

Diameter ‘D’

9 8 7 6 5 4 3 2 1

Table - 1 12

D2

2

D -D if

m

2

m-n=5

n

 =

2

D

m

-D

2

n

4 R (m-n)

MJCET Least count of the spherometer = ....................................................

Radius of curvature of the surface of the lens in contact with glass plate R .....................cm

R

l2

h

= 6h + 2

RESULT : The wavelength of the sodium light  = ................................A0 SAMPLE VIVA QUESTIONS : 1. What is principle involved in Newton’s rings. 2. What is interference. 3. What is the condition for interference maximum. 4. What is the condition for interference minimum. 5. Why Newton’s rings are circular. 6. Under what condition the central spot is bright. 7. Under what condition the central spot is dark. 8. If white light is used what kind of rings are obtained. 9. What are applications of Newton’s rings.

13

MJCET

5. LASER AIM : To determine the wavelength of laser using diffraction grating. APPARATUS: Laser diode module, grating, scale etc., SPECTROMETER

GRADUATED SCREEN

GRATING 2000 LP1

THEORY: When light is incident normally on a grating it undergoes diffraction at different angles, the observed orders of maximum are given by d sin  = n , where d = grating element = 1 /N.  = angle of diffraction n = order of maximum

 = wavelength of the laser light

N = Number of lines per cm on grating. PROCEDURE : The laser diode module is mounted horizontally. A diffraction grating (2000 LPI) is placed on a stand at the same height and adjusted for normal incidence . When laser is switched on,

we get diffraction maxima on a scale placed at about 0.5 m distance (D) with respect to grating. The

distances between different orders on left and right side (2x) are measured and tabulated. This procedure is repeated for different values of D and the results are tabulated as follows

14

MJCET Distance between Sl. grating No. and Scale (D) 50 cm

60 cm

70 cm

80 cm

Distance Distance Order of between between diffraction corresponding centre and (n) order (2x) maximum (x)

Tan = X D

Sin

Wavelength

 =

1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

Now draw graph between x and D for a given order. A straight-line graph is obtained. The slope of the graph gives tan  . i.e., slope = tan or  = tan –1 (slope) The wavelength  can be calculated as  = sin  /nN Draw graph for other order maxima also. n=4 n=3 n=2

n=1

x D

RESULT : The wavelength of the given laser beam is  = ............................ cm or A0 15

sin Nn

MJCET

6. OPTICAL FIBER- MEASUREMENT OF NUMERICAL APERTURE AIM : To determine the numerical aperture of the PMMA (Polymethyl methacrylate) cable. APPARATUS: Optic Fibre kit , D.C. Power supply, 1&3 meter FO cable, N.A Jig, adapter (9V) and connectors. PRINCIPLE: Total internal reflection THEORY: CLADDING

max

CORE

Figure - 1

The Numerical Aperature is measure of the light gathering capacity of the given optical fiber. FORMULA :

2 1/2

Numerical apperture N.A. =W/(4L +W ) 2

Acceptnace angle = m = sin -1( N.A) B LED

OPTICAL FIBER

o

A L

Figure - 2

16

W D

SCREEN

MJCET Knowing W and L, the N.A. can be calculated and substituting this N.A. value in equation (2), the acceptance angle ‘ max’ can also be calculated. DESCRIPTION : i) The Electrical to Optical Converter: It converts an Electrical input to an Optical output Po. The output Power of FO LED can be varied with the help of potentiometer knob marked “SET PO/IF” i.e. by adjusting driving current of FO LED. The FO LED driving current can be measured by connecting Digital Multimeter (DMM) leads to “Vr” sockets. Vr/47 gives the LED current in milliamps, where Vr is in millivolts.

ii) The Optical Power Meter Module: It converts the optical power coupled into the Sensor to dBm with the help of DMM and calibration conversion. Keep the DMM in 0-2000mV range. Connect the DMM Test Leads to the ‘Pout’ sockets, then the optical power in dBm is given by DMM Reading/10. As an example, if the DMM reading is-182, then the optical power ‘Pout’ is -182/10 dBm (or) -18.2dBm. PROCEDURE: The experimental arrangement is shown in figure 3.

SCREEN

PIN

The step by step procedure is as follows:

Step 1: Insert one end of either one meter length Plastic Optical Fiber Cable in the alloted knob until you feel that the fiber is touching micro lens of kit . Do not push by applying undue force that may damage micro-lens. Gently tight the nut that holds the inserted fiber firmly. Similarly connect another end to ‘N.A. Jig’ nut.

Step 2: Connect power adapter pin into the Socket ‘Vin’ and plug to 230 V AC Line. Switch on ON/OFF switch. Red light will appear at the end of the fiber in the NA kit. To set maximum output power turn ‘SET Po/IF’ knob in clockwise direction. The red light intensity will increase to it is the maximum FO LED O/P Power. Step 3: Hold the provided Scaled Screen at a distance of 10mm (L) on N.A. kit . A red spot appears on the Screen, measure the diameter (W) of the spot. (DARK ROOM WILL FACILITATE BETTER VIEWING). Substitute the measured values (L) and (W) in the N.A. formula.

N.A. =Sinmax = W/(4L + W ) Repeat the experiment for the distances of 15mm, 20mm, and 25mm etc., and note the readings in table 1. 2

2 1/2

17

MJCET S. NO.

L(mm)

W(mm)

1.

N.A

 max (Degrees)

2. 3. 4. 5.

Result:

Numerical apperture of the given optical fiber is --------------------------------

18

MJCET

7.BIPRISM-WAVELENGTH AIM: To determine the wavelength of sodium radiation.

APPARATUS: Optical bench with accessories, biprism, convex lens, sodium vapour lamp. A

S1 S S2

F

B C

PROCEDURE:

D

To get the interference fringes into the field of view of the eyepiece. Turn the slit vertical and illuminate it with sodium light. Keep the biprism at a distance of about 12 cms. from the slit. Adjust the centre of the slit , centre of biprism and centre of the eyepiece to be at the same height. By working the tangent screw, set the biprism with its edge vertical. Keep the eyepiece at a distance of about 30 cms, from the biprism. Focus the eyepiece upon the crosswires. Narrow down the width of the slit and, looking through the eye-piece, slightly rotate the biprism by working the tangent screw until alternately dark and bright interference bands appear distinctly in the field of view. On moving the eyepiece away from the biprism, the bands become broader without

moving across the field of view. If you find the bands to be moving across the field of view, it means that the vertical plane passing through the slit and edge of the biprism is not parallel to the axis of the bed. Now, move the biprism slowly at right angles to the bed until the bands remain at the centre of the field of view as the eyepiece upright is moved towards the biprism or away from it. (ii)

Determination of band width.

Keep the eye-piece at a distance of about 20 cm. from the biprism. In this position determine

the band width as follows. Take .the point of intersection of the cross-wires to one extreme of the interference pattern. Reverse the direction of rotation of the screw and set the point of intersection of

the cross wire at the middle of one bright band at the end of the field. Note the reading on the

micrometer. Continue to turn the screw in the same direction and the readings when the point of intersection is set successively at the middle of each successive bright band till nearly the end of the

pattern is reached and tabulate the observations. Next, shift the upright carrying the eyepiece through

an exactly known distance (say, 15 cm.) and repeat the observations as in the previous position. Estimate the band width.

19

MJCET (iii) To determine the distance d between the two virtual sources, S1 and S2.

Now introduce the convex lens between the biprism and the eyepiece and set it so that its

principal axis passes through the centres of the slit, the biprism and the eye-epiece. Then move the eyepiece away so that the distance between the slit and the eyepiece is more than four times the focal

length of the convex lens. Hold a piece of paper just in front of the eyepiece and shift the lens close to

the biprism till the magnified images of S1and S2 are caught on the paper. Sometimes it may so happen that the uprights carrying the biprism and lens do not allow them (biprism and lens) to get close enough to get magnified images on the screen. In such a case keep the lens close to the biprism and bring the

slit nearer to the biprism until the magnified images of the slit are seen on the paper. Now, remove the paper and move the eyepiece to observe the magnified images of the slit.

Turn the micrometer screw until the point of intersection of the cross-wires is taken much beyond

the two images. Then reverse the direction of motion and set the point of intersection of cross-wires

at the middle of the first image and note the micrometer reading. Next continue to rotate the micrometer screw in the same direction until the point of intersection of the cross wires is brought to the middle of the second image and again note the reading. The difference of the two readings gives the distance (d1) between the two magnified images.

Now, keeping the eyepiece in the same position move the upright carrying the convex lens until

well-defined diminished images of the slit are formed in the plane of the cross- wires. With the

micrometer measure the distance (d2) between the diminished image of the slit. The required distance

d1 d2

d between S1 and S2 is given by the formula d = OBSERVATIONS : (i)

1. Determination of fringe width

With eyepiece in one position at distance D1 from the slit.

Least count of the micrometer screw........ Serial No. of bright band 1 2 3 4 5

Micrometer Reading (a)

Serial No. of bright band 6 7 8 9

10 20

Micrometer Reading (b)

Width of 5 bands (a - b)

MJCET Mean width of a band  1  (ii)

With eyepiece in another position at a distance D2 (say D1 + 15 cms.) from the slit.

Serial No. of bright band 1

Micrometer Reading (a)

2

Serial No. of bright band 6

Micrometer Reading (b)

Width of 5 bands (a - b)

7

3

8

4

9

5

Mean width of a band  2  2.

10

To find distance (d) between the virtual sources i.e. between S1 and S2

Least count of the micrometer screw ……..

Nature of images

Readings when point of

intersection of cross-wire is on 1st image

on 2nd image

d1

Magnified

d2

Diminished Actual distance between S1 and S2 = (d) =

Distance between two images

d1 d2

Then calculate wavelength of the radiation of source from the formula D2 – D1 is simply given by the difference in the readings of the 1st and 2nd positions of the micrometer upright.

PRECAUTIONS:

1. The lateral shift should not be there.

2. The distance between the slit and the eyepiece should be more than 4f of the lens. 3. The micrometer screw should be rotated in only one direction.

21

MJCET

8. ULTRASONIC INTERFEROMETER AIM : To determine the velocity of Ultrasonic waves in liquids. APPARATUS : A high frequency generator, measuring cell, shielded cable and given liquids. DESCRIPTION : The experimental setup consists of two parts. 1. 2.

A high frequency generator A measuring cell.

The high frequency generator is designed to produce ultrasonic waves of frequency 1MH z/2 MHz. This generator excites the quartz crystal fixed at the bottom of the measuring cell. The quartz crystal is of suitable size so that it vibrates generating ultrasonic waves in the experimental liquid filled in the measuring cell. A micrometer is fixed to observe the changes in current and two controls for the purpose of

sensitivity regulation and initial adjustment of the micrometer are provided on the panel of the high frequency generator.

Micrometer

Reflector Experimental Liquid Quartz Crystal R.F. Input THE MEASURING CELL

THE MEASURING CELL The measuring cell is a double walled cell for maintaining the temperature of the liquid constant during the experiment. A fine micrometer screw has been provided at the top which can lower or raise the reflector plate in the liquid in the cell through a known distance.

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MJCET

PRINCIPLE : Ultrasonic waves of known frequency (f) are produced by a quartz crystal fixed at

the bottom of the cell. These waves travel through the liquid and are reflected by a movable metallic plate kept parallel to the quartz crystal. If the separation between these two plates is exactly an integral

multiple of half wavelength. Standing waves are formed in the medium. This acoustic resistance gives rise to an electrical reaction on the generator driving the quartz crystal and the anode current of the generator becomes maximum.

If the distance is now increased or decreased by integral multiple of one half wavelength, anode current becomes maximum. From this distance we can know the wave length of the ultrasonic wave in the liquid. The Velocity can be calculated using Velocity = frequency x wavelength. PROCEDURE : The instrument is adjusted in the following manner. 1.

Insert the cell in the square base socket and clamp to it with the help of a screw provided on

2.

Unscrew the knurled cap of cell and lift away from double walled construction of the cell. In

3.

In the double walled cell there is provision for water circulation to maintain desired temperature.

4.

Connect the high frequency generator to the cell by co-axial cable provided with the instrument.

5.

For initial adjustment two knobs are provided on high frequency generator one is marked with

one of its sides.

the middle portion of it pour experimental liquid and screw the knurled cap.

‘Adj’ & the other with ‘Gain’. With knob marked ‘Adj’ the position of the needle on the  ammeter is adjusted and the knob marked ‘Gain’ is used to increase the sensitivity of the

instrument for greater deflection if desired. The meter is used to notice the number of maximum deflections while reflector is moved up and down in liquid. 6.

The ultrasonic waves move normal from the quartz crystal till they are reflected back from the movable plate and the standing waves are formed in the liquid in between the reflector plate and the quartz crystal.

The Micrometer is slowly moved till the anode current on the meter of the high frequency generator shows a maximum.

The initial reading on the micrometer R1 is noted. The micrometer is moved until we get ‘n’ such maxima. The final reading R2 is noted. The difference of these two readings ‘d’ is found out. The wavelength of the ultrasonic wave is calculated using   2d mm

n

The velocity of the ultrasonic wave in the liquid is calculated using V =  .f , where f is the frequency of the generator. The readings may be entered as follows. 23

MJCET OBSERVATIONS : Sl.

No.

Initial reading of the Micrometer (R1) mm

No. of maximum deflections in Ammeter (n)

Final reading of the micrometer R2 mm

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Total distance moved (d=R2R1) mm

Wavelength

2d

 = 1000.n m

Velocity V=f  m/s

MJCET PRECAUTIONS : 1.

Do not switch on the generator without filling the experimental liquid in the cell.

2.

Remove experimental liquid out of cell after use, keep it clean and dry.

3.

Keep micrometer open at 25 mm after use.

4.

Avoid sudden rise or fall in temperature of circulated liquid to prevent thermal shock to the

5.

While cleaning the cell care should be taken not to spoil or scratch the gold plating on the quartz

quartz crystal. crystal.

RESULT : The average velocity of Ultrasonic waves in the given liquid = ............................m/s.

SAMPLE VIVA QUESTIONS : 1. What are ultrasonic waves. 2. What are infrasonic waves. 3. What are the limits of audibility. 4. What is piezoelectric effect. 5. What are different methods of producing ultrasonic waves. 6. How much is the velocity of ultrasonic waves in air. 7. Is the velocity of ultrasonic waves same in all material media. 8. Can ultrasonic waves travel in vacuum. 9. What is the principle of the present experiment.

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MJCET

9. VERIFICATION OF MALUS LAW AIM : To verify the malus law using polarization. APPARATUS : Malus law kit, digital volt meter and connecting wires

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MJCET OBSERVATION:

Angle voltage Angle voltage 0

100

20

120

40

140

60

160

80

180

10

110

30

130

50

150

70

170

90

190

Angle voltage Angle voltage 200

300

220

320

210 230 240 250 260 270 280 290

Voltage

MODEL GRAPH :

A n g le ( d e g r e e s )

RESULT:

Malus Law verified

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310 330 340 350 360