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Sapkal Knowledge Hub
Kalyani Charitable Trust’s
Late G. N. Sapkal College of Engineering
Kalyani Hills, Anjaneri, Trimbak Road, Nashik - 422212.
Ph. : 02594 - 220171 /172 /173 /174 /175
Applied PhysicsSemister -I
Academic Year20 - 20
Kalyani Charitable Trust’s
Kalyani Charitable Trust’s
Late G. N. Sapkal College of Engineering
Kalyani Hills, Anjaneri, Trimbak Road, Nashik - 422212.
Ph. : 02594 - 220171 /172 /173 /174 /175
CERTIFICATEThis to certify that
Mr./Miss...........................................................................................................................................................
.................................. of Glass...................................Div...................................Roll No.................................
University Examination No....................................................has completed satisfactorily experiments /
practical work in Applied Physics as prescribed by University of Pune, during the semester -I of academic
year 20 - 20
Date: / /20
Sub Incharge Head PRINCIPAL
Applied Physics Deptt. of Applied Science
Kalyani Charitable Trust’s
Kalyani Charitable Trust’s
Late G. N. Sapkal College of Engineering
Kalyani Hills, Anjaneri, Trimbak Road, Nashik - 422212.
INDEXExpt. No. Title of Experiment Date Page No. Remark & Sign
1. To determine wavelength of unknown color using Diffraction Grating.
2. To determine the radius of curvature of a planoconvex lens using Newton's rings
3. To determine the resolving power of a telescope.
4.To study the use of C.R.O. for themeasurement of voltage, frequency and Lissajous figures.
5. e/m of an Electron Using Bar Magnet Method (Thomson's Method)
6.To determine the speed of ultrasonic waves in a given medium using ultrasonic interferometer.
Date of experiment : / / .
Signature of teacher with date
EXPERIMENT NO: 1TITLE : Diffraction Grating
Evaluation
Timely/late : /2Performance : /2Understanding : /3Lab Quiz : /2Neatness : /1--------------------------------------
Total marks : /10
Aim : To determine wavelength of unknown color using Diffraction Grating.
Apparatus : Spectrometer, mercury lamp, diffraction grating, magnifying glasses, etc.
Diagram :
Formula : We know that,(a + b) sin0 = nλ,
λ=(a + b)
nsin0
where, (a + b) = grating elementa = width of a slitb = distance between two adjacent slitsn = order of the spectrum
% error = λexp _λstd
______________
λstd
X 100
Where, λexp = experimental value of wavelengthλstd = standard value of wavelength
Theory :
Spectroscopy is a powerful research technique in Physics. It is useful for production, observation, analysis
and interpretation of the spectra of given sources. The properties of a spectral source can be studied by
calculating parameters like intensity, line width and wavelengths of the spectral lines.
Spectroscopy has been found applicable in determination of atomic and molecular structures and
energy levels, study of interatomic and intermolecular interactions, identification of elements,
identification of chemical compositions of unknown substances and their physical properties, etc.
Verification of Bhor’s model of the atom has been made possible due to spectroscopic analysis.
Spectroscopy is also an important research tool in Astrophysics where it is used for studying the
compositions of planets and stars, their atmosphere, as well as their physical properties like pressure,
density, temperature, etc. The fact that the sun is composed of 65 % helium and 35 % hydrogen has been
discovered using spectroscopic analysis.
The aim of the experiment is one of the basic tasks in spectroscopy i.e. determination of
wavelength of spectral lines. The distribution of dispersed radiated energy arranged periodically according
to certain parameters like energy, frequency, wavelength, etc.is called the spectrum. The source can be
made to emit the radiation by suitably exciting it by direct or electrical heating. The excited atoms re-emit
the absorbed energy while returning to the ground state. This radiated energy can be converted into a
spectrum using the spectrometer which is an instrument used to produce, observe and analyze the
spectrum of a given source. It consists mainly of a collimator, a spectroscopic device, and a telescope.
The bending of any kind of wave when encountered by any obstacle of dimension comparable to
its wavelength is called diffraction. A diffraction grating consists of a large number of exactly parallel and
equidistant slits. The grating diffracts the light waves of various wavelengths emitted by the source
through different angles, thereby making it possible to determine the wavelengths. Gratings are often used
to measure wavelengths and to study the intensity of spectral lines.
Using mathematical analysis, it can be shown that the principal maxima of order ‘n’ for a given
grating lies at an angle ‘9’ which satisfies the following condition :
(a + b) sin0 = nλ
where, (a + b) = grating element
a = width of a slit
b = distance between two adjacent slits
n = order of the spectrum
The source used in this experiment is a mercury vapour lamp, which is a source of white light. It
contains vapours of mercury in which electric discharge is produced by applying high voltage. The mercury
spectrum consists of a few lines in the ultraviolet region and a few lines in the visible region.
Procedure:
1) Adjust the telescope and collimator for parallel rays by Schuster’s method.
2) Mount the diffraction grating on the prism table such that its plane is perpendicular to the
prism table.
3) Arrange the face of the grating so that it lies normal to the collimator.
4) Focus the vertical cross-wire of the eye-piece perfectly on the first (violet) line of the first
order spectrum of left side. This focusing must be perfect for accurate results.
5) Clamp the telescope and note its angular position using the angular scale through the observation window. Use a reading lamp and magnifying glass to note the reading.
6) Similarly, take readings for the other lines of spectrum. These readings are 01.
7) Turn the telescope to the right side and take the readings for the first order spectrum on this side. These readings are 02.
8) Calculate 20, 0, sin0 and therefore λ for each color by using the given formulae.
9) Compare your results (experimentally calculated wavelengths) with standard values and calculate how much the results deviated from standard ones by using the formula for percentage error.
Observations:
i) Grating element (a + b) =
2.54
------------
15000
= . . . . . . . . . . . . . . . . . cm
ii) Least count of spectrometer = . . . . . . . . . . . . . . . . .
Observation Table:
Obs.No.
Color of the
Spectral line
Angular Positions
20=01-02 0=20/2 sin0 λexp λstd A0 %error
Left 01 Right 02
1. Violet 4387
2. Green 5460
3. Yellow 5890
4. Red 6390
Sample Calculation:
Result:
Wavelength of the unknown color is . . . . . . . . . . . . . . . . . . . . . . . . .
Conclusion:
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Date of experiment : / / .
Signature of teacher with date
EXPERIMENT NO: 2TITLE : Newto’s Rings
Evaluation
Timely/late : /2Performance : /2Understanding : /3Lab Quiz : /2Neatness : /1---------------------------------------
Total marks : /10
Aim : To determine the radius of curvature of a planoconvex lens using Newton’s rings.
Apparatus : A traveling microscope with long focus objective, Newton’s rings apparatus, amagnifying glass, reading lamp, sodium lamp.
Diagram :
Formula:
R =Slope
---------4λ
where, R = radius of curvature of planocovex lens
λ = wavelenghth of sodium light (5893 A)
Theory:
When a planoconvex lens is placed over a glass plate, a thin wedge shaped film is formed between the two glass surfaces. When illuminated by a beam of monochromatic light, interference takes place between the rays reflected from the lower surface of the lens and the upper surface of the glass plate (i.e., top and bottom surfaces of the air film). The interference pattern is in the form of circular fringes. The fringes are the locus of points of constant thickness of the air film.
The surfaces of the lens and the glass plate should be perfectly clean. The glass plate on which the lens is placed should be optically flat and the curved surface of the planoconvex lens must be perfectly spherical, in order to be able to observe the circular rings. Otherwise the fringes are irregular in shape. Newton’s rings pattern when observed in the reflected light has a dark center. This is because at this position the lens and the plane glass plate touch each other and the thickness of the air film is zero. In the reflected light, the wave getting reflected at the surface of the denser medium has an additional phase shift of radians, and hence the path difference corresponding to λzero thickness is always ----- 2
In case some dust particles are present on the surfaces, the two surfaces do not have a perfect contact at the center leading to a bright spot at the center of the pattern. If both the surfaces are cleaned and rearranged we get a dark-spot.
The concentric alternated dark and bright rings in the Newton’s rings pattern are numbered according to the following convention. The central dark spot in the pattern is called the ‘zeroth dark ring.’ This is followed by the ‘first bright ring’, which in turn is followed by the ‘first dark ring’. The next ring is bright and is the ‘second bright ring’. Then comes the ‘second dark ring’, and so on.
By theory, we know that the radii of dark rings are proportional to the square root of even natural numbers, whereas those of the bright rings are proportional to the square root of odd natural numbers. This fact is made use of in the present experiment.
Procedure:
1) Arrange the apparatus as shown in the Fig. Clean the lens and glass plate thoroughly and then place the planoconvex lens on the glass plate. With its convex surface touching the plate, place it below the microscope.
2) Allow the parallel light from sodium lamp to be incident on a glass plate, which is held at 45 degrees to the horizontal so that the reflected light falls upon the lens. Adjust the position of the microscope so that the point of contact is just below the microscope objective. Focus the microscope until the rings are distinctly visible and the center of ring system lies below the point of intersection at the cross wires. Rotate the eyepiece so that one of the cross wires is perpendicular to the horizontal scale.
3) Move the microscope across the field of vision and focus it on a distinct dark ring, say, the 20th dark ring from the center on the left. Read the position of the microscope with the cross wire tangential to the ring. Focus on successive dark rings in steps of two and note the corresponding positions of the microscope. Continue this till you reach dark ring number 4. While focusing take care that every time the cross wire remains tangential to the ring.
4) Move the microscope across the center until it is focused at the other end of the diameter of the dark ring number 4. Read the position of the microscope and proceed onwards until you reach 20th dark ring on the right. From the set of readings, diameters Dn of the rings can be determined.
5) Calculate Dn2 and plot a graph of Dn2 Vs. ring number, n. Calculate the slope of the straight line and knowing the wavelength of sodium light, calculate the radius of curvature of the planoconvex lens using the given formula.
Observations:
L.C. of traveling microscope =..............
Observation Table:
Obs. No.
No. of dark rings (n)Microscope reading (cm) Diameter (cm)
Dn - x1 - x2 Dn2 (cm2)Left (x1) Right (x2)
1
2
3
4
5
6
7
8
9
10
Nature of the Graph:
Sample Calculation:
Slope of the graph =Dn2 - Dm2---------------
4λ
R =Slope
---------4λ
Result :
Radius of curvature of the planoconvex lens is . . . . . . . . . . . . . . . . . . . . . . . . .
Conclusion :
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Date of experiment : / / .
Signature of teacher with date
EXPERIMENT NO: 3TITLE : Resolving Power of Telescope
Evaluation
Timely/late : /2Performance : /2Understanding : /3Lab Quiz : /2Neatness : /1---------------------------------------
Total marks : /10
Aim : To determine the resolving power of a telescope.
Apparatus : Telescope with adjustable slit, a black cardboard with narrow white strip on it,
traveling microscope and meter scale.
Diagram :
Formula: 1 λi) Theoretical resolving power = ----- , where 0 = ----- 0 a 1 λi) Practical resolving power = ----- , where 0 = ----- 0 a
where λ = wavelength of light used a = width of the rectangular slit for just resolution of two objectsd = separation between two objectsD = distance of the objects from the objective of the telescope
λ dHence, = ----- = ----- a D
Theory:
Meaning of resolving power:
When the two objects are very near to each other or they are at very large distance from our eye,
the eye may not be able to see them as separate. If we want to see them separate, optical instruments such as
telescope, microscope etc. for close objects and prism and grating etc. for spectral lines are employed. Even
if we assume that the instruments employed are completely free from all optic defects, the image of a point
object or line is not simply a point or line but it is a diffraction pattern with a bright central maximum and
other secondary maxima having minima in between of rapidly decreasing intensity. Thus an optical
instrument is said to be able to resolve two point objects if the corresponding diffraction patterns are
distinguishable from each other. The ability of the instrument to produce their separate patterns is known as
resolving power.
Rayleigh’s criterian for resolution:
According to Rayleigh’s criterion, two point sources are resolvable by an optical instrument when
the central maximum in the diffraction pattern of one falls over the first minimum in the diffraction pattern
of the other and vice versa. Similarly in case of spectral lines of two different wavelengths, the lines will be
resolved when the central maximum due to one wavelength falls over the first minimum due to other and
vice versa.
In order to illustrate the criterion let us consider the resolution of two wavelengths λ1 and λ2 by a grating. Fig. 1(a) shows the intensity curves of the diffraction patterns of two wavelengths. The difference in wavelengths is such that their principal maxima are separately visible. There is a distinct point of zero intensity in between the two. Hence the two wavelengths are well resolved.
Now consider the case when the difference in wavelengths is smaller and such that the central
Principal Principal Maximum Maximum
maximum of wavelengths coincides with the First minimum of the other as shown in Fig. 1 (b). The resultant intensity curve is shown by thick curve. The curve shows a distinct dip in the middle of two central maxima, i.e., there is a noticeable decrease in intensity between the two central maxima indicating the presence of two different wavelengths. Thus the two wavelengths can be distinguished from one another and according to Rayleigh they are said to just resolved.
Again consider the case when the difference in wavelengths is so small that the central maxima corresponding to two wavelengths come still closer as shown in Fig. 1(c). The resultant intensity curve in this case is quite smooth without any dip thus giving the impression as if there is only one wavelength source although somewhat bigger and stronger. Hence the two wavelengths are not resolved.
Thus the two spectral lines can be resolved only dip to a certain limit expressed by Rayleigh criterion.
Resolving Power of Telescope:
A telescope is used to see the distinct objects. The details which it gives depend on the angle
subtended at its objective by two point objects and not on the linear separation between them. The resolving
power of a telescope is defined as the reciprocal of the smallest angle subtended at the objective by the two
distinct object points which can be just seen as separate ones through the telescope.
Expression for the resolving power:
Let d be diameter of the objective of tire telescope Fig. 1(d). Consider the incident rays of light from two
neighboring points (say two stars lying very close to each other, not shown in the figure). Suppose d0 is the
angle subtended by the two distant objects at the objective of the telescope. The ring supporting the
telescope objective and the lens itself serve as a circular aperture and produce Fraunhofer diffraction
patterns in the focal plane of the objective. Let P1 and P2 be the positions of the central maxima of the two
images. The pattern will tie very close to each other with a large amount of overlapping. If the overlapping
is too much, the telescope may not be able to distinguish them as separate. According to Rayleigh’s
criterion, the patterns will be just resolved if the central maxima of one just falls on the first minima of the
other.
Now the secondary waves traveling in direction AP2 and BP2 meet at P2 and have a path
difference equal to (BP2 - AP2) = BC.
From Fig. 1(d),
BC = AB sin d0 = AB . d0 (for small angles)
= d. d0
If this path difference d . d0 = λ, the position of P2 corresponds to the first minimum of the first image. But P2 is also the position of the central maximum of the second image. Thus Rayleigh’s condition of resolution is satisfied if,
λd. d0 = λ, or d0 = ----- ------------------------(1) d
The above idea may be understood in the following way:If we consider that the whole wave front AB is divided into two halves AO and OB, then the
path difference between the secondary waves from the corresponding points in the two halves is λ----- All the secondary waves from the two halves interfere destructively with one another and hence P2 dcorresponds to the first minimum of the first image.
The condition (1) holds good for rectangular aperture. According to Airy, this condition in case of a circular aperture can be expressed as
1.22λd0 = ------------ ------------------------(2) dd0 represents the minimum resolvable angle between the two distant point objects or this gives the
limit of resolution of the telescope. The reciprocal of d9 measures the resolving power of the telescope. Hence
1 d----- = ------------ Thus a telescope with large diameter of objective has a higher resolving power. d0 1.22λ
Procedure:1) Mount the telescope on a stand such that its axis lies horizontal and the rectangular lines
marked on cardboard or glass on the another stand such that they are vertical. Place the two stands at a suitable distance.
2) Then illuminate the object with the source of light (sodium lamp).3) Now open the slit with the help of micrometer screw and move the telescope in the
horizontal direction such that the images of two vertical sources are in the field of view of the eye piece.
4) Then reduce the width of the slit step by step till the two images just ceases to appear as two and note down the reading of the micrometer.
5) Then close the slit completely and note down the micrometer reading. This gives the width of slit (a). OR If the slit is not provided with micrometer arrangement, the slit is gradually reduced till the two images ceases to appear two. Take the slit and measure its width with the help of traveling microscope.
6) Then measure the width of white or black rectangular strips with the help of traveling microscope i.e. (d).
7) Then measure the distance between the object and the slit which gives D.8) The experiment is repeated for different values of D.
Observations:Wavelength of the source of light (Sodium source) = λ = 5893 A0
Distance between the two slits (a) = 1mm = 0.1cmLeast count of screw = . . . . . . . . . . cm
Observation Table:
Obs. No.
Width of the Slit (a) cm
Distance between the slit & collimator
(D) (cm)
Theoretical Resolving power
λ__D
Practical Resolving power
λ__a
1
2
3
4
5
Sample Calculation:
1 λi) Theoretical resolving power = ----- , where 0 = ----- 0 a
1 dii) Practical resolving power = ----- , where 0 = ----- 0 D
Conclusion :
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Date of experiment : / / .
Signature of teacher with date
EXPERIMENT NO: 4TITLE : Cathode Ray Oscilloscope (C.R.O.)
Evaluation
Timely/late : /2Performance : /2Understanding : /3Lab Quiz : /2Neatness : /1
----------------------------------------- Total marks : /10
Aim : To study the use of C.R. O. for the measurement of voltage, frequency and Lissajous figures.
Apparatus : Dual trace C.R.O, Function generator, connecting wires etc.
Diagram :Cathode Ray Tube (CRT):
Procedure:Voltage Measurement:
1. Connect the cords to the C.R.O. and function generator.2. Select the signal from the function generator and give the input signal to the C.R.O.3. Select the sine wave and adjust the wave on the screen with the help of voltage sensitivity
and time per division.4. Measure the signal on Y-axis i.e. voltage peak to peak (Vpp) and multiply the value of voltage
sensitivity.5. Keep the input frequency constant from the function generator and take the readings for
different voltages.6. Match the input voltage and measured voltage from the C.R.O.
Observation Table:
Input frequency = ............................
Obs. No.
Vpp
in divVoltage sensitivity
Measured Voltage volt
I/P voltage volt
1
2
3
4
5
Frequency Measurement:
1. Connect the cords to the C.R.O. and function generator.
2. Select the signal from the function generator and give the input signal to the C.R.O.
3. Select the sine wave and adjust the wave on the screen with the help of voltage sensitivity
and time per division.
4. Measure the signal on X-axis i.e. Frequency peak to peak (lpp) and multiply the value of time
per division.
5. Keep the input voltage constant from the function generator and take the readings for
different frequencies.
6. Match the input frequency and measured frequency from the C.R.O.
Observation Table:
Input voltage = ............................
Obs. No.
Ipp
in divTime per division (T)
in sec.
1F = ---- Tin Hz
I/P Frequency in Hz
1
2
3
4
5
Signal measurement with help of Lissajous figures.Procedure:
1. Connect the cords to the C.R.O. and function generator
2. Give the signal from the two function generator to obtain the Lissajous figures.
3. Swap both the input signal by keeping input voltage constant.
4. Observe the various Lissajous figures for different frequencies.
5. Calculate the input and output frequency with the help of following formula.
Formula: y F = ----- x Fin
X
where, y = no. of points on Y-axis.x = no. of points on X-axis. Fin = input frequency.
Observation Table:Input frequency (Fin ) = ............................
Obs. No.
Lissajous figures.No. of points of
contact on X-axisNo. of points of
contact on Y-axisFrequency in Hz
1
2
3
4
Date of experiment : / / .
Signature of teacher with date
EXPERIMENT NO: 5TITLE : e/m of an Electron Using Bar Magnet Method (Thomson’s Method)
Evaluation
Timely/late : /2Performance : /2Understanding : /3Lab Quiz : /2Neatness : /1
----------------------------------------- Total marks : /10
Aim : To calculate the charge to mass ratio (e/m) of an electron using Thomson’s method.
Apparatus : Thomson’s tube. Power supply, magnetometer, two bar magnets, etc.
Diagram :
Theory:The ratio e/m of an electron was first invented by J.J. Thomson in 1897. His relevant experiment based on the principle that cathode rays are deflected by magnetic and electric field. This experimental arrangement mainly consists cathode ray tube. When a high potential difference is applied between anode and cathode, of cathode rays tube. Pencil like electron beam is obtained using two metallic plates kept at high positive potential as shown in Figure (1). The beam strikes normally on the surface of the CRT
Deflection of cathode rays due to magnetic field:
First of all, the electric and magnetic fields are switched off. The position of the spot on the screen for undeflected rays is noted. Then apply magnetic field in a direction perpendicular to the direction of motion of electrons using bar magnets or electromagnets. Let B be the intensity of magnetic field, e charge on each electron, and v, the velocity of electron. Due to magnetic field, force B e v is acted up on the electron. The direction of this force will be in a direction perpendicular to the motion of electrons and magnetic field. Hence the path of electron becomes circular. After magnetic field electron come out in a straight line. Let r be the radius of the circular path, then the centripetal force on the electron is given as mv2/r where, m is mass of the electron. This force is balanced by already available force (magnetic force) on the electron i.e. Bev. Where, B is the magnetic field acting on the electron. Hence, Bev = mv2/r or e/m = v/Br. Knowing the value of of r and v e/m can be computed. Also we know that, force due to electric field = force due to magnetic field.
Ee = Bevv =E/B
where,e = charge of an electronE = applied voltagev = velocity of electron
Let d be the distance between two plates and if V is the P.D. applied between two plates, then E = V/d, hence above equation becomes v = V/B.d.Again electric field is remove and only magnetic field applied. Under this field deflection of the spot in downward direction and it is then measured, i.e path of the electron in circular manner which having radius say r. Therefore force due to magnetic field is balanced by centripetal force acting on Bev = mv2/r and e/m = v/B2Rd.
In this case ‘r’ can be calculated by using proper geometrical method (path of the electron under magnetic field. (See figure 2). Thus and e/m can be computed. In the laboratory all the standard data and manufacturing details of CRT is colleted and then e/m will be accurately calculated.
Procedure:1. Using magnetometer fix the north- south direction. Also draw the N-S line on the plane table.
Place the CRT on wooden in the N-S direction so as to reduce the effect from earth’s magnetic field.
2. Using proper special power supply make the proper connections and on the power supply, wait! until intense spot will appear on the screen of the CRT.
3. Apply D. C. voltage so that vertical deflection of the spot of the CRT takes place. Place the bar magnets symmetrically with scale arrangement as shown in figure. Make the position of the bar magnet such away that spot should i.e. E and B should be nullified.
4. Off the power supply and carefully remove the CRT carefully. Put the magnetometers on wooden stand and adjust magnetometer box correct on the line joining two magnets. In this situation just move magnetometer box towards screen, in result magnetic needles shows deflection say ɸ1 and ɸ2 . Find Bav and b, calculate (1-x) and plot the graph of b(l-x) versus x find the area under the curve.
5. Note down detail observation from the data sheet of CRT also note down some constants carefully. Using formula calculate the e/m.
Observations:1) Length of deflection plate (P) = 2 cm
2) Spacing between deflection plates (D) = 0.4 cm
3) Spacing between deflection plate and screen (L) = 16 cm
4) Distance between screen and slit. (l) = 14 cm
5) Horizontal component of earths magnetic field.(H’) = 0.37 Gauss.
6) Plate voltage (v) =.. . . . . . . . .V
7) Defection with respect to voltage (y) = 1 cm
Observation Table:
Obs No.
ɸ1 (deg.) ɸ2 (deg.)ɸ =
(ɸ1+ tanɸH
=H’ tanɸ(gauss)
h = H-Hav
(gauss)(I-x) h(I-x) 0.512 Hav
⌠h(I-x)dx= area
under curve
Formulae:1. To find electric field in e.m.u.
Voltage in e.m.u. (V) = v (volts)X108=. . . . . . . . . . . . . . . . . . . . . . . . . . . e.m.u.
Electric field E=voltage in e.m.u.
____________________distance between plate
V= ___ =
D. . . . . . . . . . . . . . . . . . . . . . . . . . . e.m.u.
2.
V ---
∫[∫H.dx] dx = ___ = l2
Hav
D
+ area under curve =. . . . . . . . . . . . . . . . . . . . . . . . . . . gauss-cm2
3. P -- {--- + L}.P x E 2Velocity = -----------------------
∫[∫H.dx]dx =. . . . . . . . . . . . . . . . . . . . . . . . . . . cm/sec
4. e V.Y ___ = _________
m ∫[∫H.dx] dx
=. . . . . . . . . . . . . . . . . . . . . . . . . . . coloumb / gm
Sample Calculation:
Conclusion :
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Date of experiment : / / .
Signature of teacher with date
EXPERIMENT NO: 6TITLE : Ultrasonic Interferometer
Evaluation
Timely/late : /2Performance : /2Understanding : /3Lab Quiz : /2Neatness : /1--------------------------------------
Total marks : /10
Aim : To determine the speed of ultrasonic waves in a given medium using ultrasonicinterferometer.
Apparatus : Ultrasonic interferometer, liquid (distilled water), high frequency generator, Co-axial shielded cable to connect high frequency generator to the measuring cell of the interferometer.
Diagram :
Theory:
An ultrasonic interferometer offers a direct method of determining the speed of ultrasonic wave in
liquids. The measurement is based on accurate determination of the wavelength in the given medium.
Ultrasonic waves of known frequency are produced by a quartz crystal, which is fixed at the bottom of the
cell. These waves are reflected by a movable metallic plate, which is kept parallel to the quartz crystal. If the
separation between these two plates is exactly a whole multiple of the wavelength, standing waves are
formed in the medium. This creates an electrical reaction in the generator, which drives the quartz crystal.
As a result, the anode current of the generator becomes maximum. If the distance is increased or decreased
λ— or a multiple of it, the anode current becomes maximum. The velocity of ultrasonic wave can be 2calculated from the knowledge of the wavelength.
Formula:
v = f.λ
where, v = speed of ultrasonic wavesf = frequency of wave
d λ = wavelength of wave = 2 ___ n
d = distance of the reflector plate from the quartz crystal plate
n = number of deflections in the ammeter when the reflector plate moves through the
distance d
Procedure:1) Insert the cell in the square base socket and clamp it with the help of the screw provided on
one of its sides.2) Unscrew the curled cap of the cell and lift it away from the double wall. Pour the liquid in
the screw on the cap. The scale should be in front of observer.3) Connect the high frequency generator to the measuring cell using the cable provided.4) For the initial adjustment, two knobs are provided on the high frequency generator, one is
marked (Adj) and the other is marked (Gain).5) Switch on high frequency generator and wait for 15 sec to warm it up. Initially, the needle of
the ammeter goes to maximum, indicating that the ultrasonic waves are produced.6) Adjust the needle to the neutral position (at 50 A) using adj knob. Keep the sensitivity (using
the gain knob) such that the needle goes to 60 A.7) Keep the micrometer on exactly 10 mm.8) Keep the micrometer screw moving slowly so that the reflector plate is moved upwards.
nλ Carefully observe the ammeter scale. Whenever the condition d = ____ is satisfied, 2the current will peak and the ammeter will show maximum deflection of the needle. Immediately stop at this stage and note the reading on the scale. This is the first reading.
9) Continue rotating the micrometer screw. Every time the instrument satisfies the above condition, the ammeter needle will show maximum deflection. Continue rotating the screw while counting the number n of deflections. Stop immediately after the chosen value of n and note down the micrometer reading.
10) Calculate the speed of ultrasonic waves using the given formula.
Observations:1) Liquid used = distilled water2) Frequency applied = 2 x 106 Hz3) Least count of micrometer = .........cm
Observation Table:
Obs. No.
No. of deflections (n)Micrometer
readingd1 (mm)
Micrometer readingd2 (mm)
d2 - d1
(mm) 2dn = ------ n(mm)
v = f. λ(mm / s)
1
2
3
4
5
6
7
8
9
10
Calculation:
Result:
The speed of ultrasonic waves in the given liquid is.................m/s.
