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7/30/2019 physics manual sem1
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Applied Physics TSEC
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DIFFRACTION GRATING (WHITE LIGHT)
Aim To determine the unknown wavelength of the spectrum of a given source
using plane diffraction grating.
Apparatus Mercury lamp, diffraction grating, spectrometer, prism.
Formula For diffraction grating
e = n/Sin
where e grating element
n order of spectrum
wavelength of the light
angle of diffractionTheory Refer to applied physics book.
Experimental Arrangement
Procedure
1. Illuminate the slit of the spectrometer by mercury light. Using the given prism, levelthe prism table by optical method.
2. Adjust the telescope and the collimator for parallel light.3. Mount the grating on the prism table for normal incidence as follows. Fix the grating
holder on the prism table with its plane vertical coinciding with centre of the table.
The ruled surface of the grating facing the telescope. Place the collimator and the
telescope in line so that the direct image of the slit falls on the cross wire. Take the
window readings. Turn telescope through 90
0
so that the axes of the collimator andtelescope are mutually perpendicular. Rotate the prism table till a reflected image is
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formed on the cross wire. Take the reading in the same window. The brighter of the
two images observed should be on the cross wire. Adjust the tow sources on both the
sides of the grating to make the image symmetrical. Take the reading in the same
window and turn the grating through 450
and 1350
such that the ruled side is towards
the telescope and fix it.4. Set the telescope to receive first order image of the spectrum on LHS and RHS.Determine grating angle for every colour and hence determine its wavelength.
5. Plot graph of vs . Find for unknown wavelength (green colour) and hencedetermine the wavelength.
Observation Table
Least count of the spectrometer = 1 (one min.)
Grating element = 2.54/15000 cm/line
Colours
Spectrometer reading
xx yy Mean2
Wavelength A
0
LHS RHS
x y x y
Red
Yellow
Green
Greenish Blue
Blue
Bluish Violet
Violet
Result The unknown wavelength (from graph) is = _______________ A0
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NEWTONS RING
Aim To find the radius of curvature R of the given plano-convex lens by
Newtons Rings method.
Apparatus Plano-convex lens of large focal length, plane glass plate, black paper, sodiumsource, microscope, collimating lens, reading lamp.
Formula Radius of curvature formula
cm
where dn diameter of the nth
ring.
dm diameter of the mth
ring.
wavelength of the light employed.
Theory Refer to applied physics book.
Experimental Arrangement
Procedure
1. Clean the apparatus; it should be free of dust.2. Find the focal length of the convex lens.3. Put on the sodium light source and place this lens at focal length distance from the
source.
4. The parallel beam of monochromatic light, obtained from the extended source, fallson the glass plate placed at 45
0.
5. Light reflected from the glass plate G is incident normally on the plano-convex lens Lmounted on the optically flat glass plate P.
6. Now light is reflected upwards from the upper & lower face, wedge shaped air filmenclosed between the plano-convex lens L and the glassplate P.
7. The reflected light rays have path difference which depends on the thickness of the airfilm at the point of incidence.
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Applied Physics TSEC
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RYDBERGS CONSTANT
Aim To determine Rydbergs constant using calibration curve of Hg source.
Apparatus Spectrometer, prism, spirit level, mercury lamp, hydrogen tube.
Theory Refer to applied physics book.
Procedure
1. Adjust the spectrometer for parallel light Illuminate the slit with mercury source.Adjust the prism at minimum deviation for any colour and fix the prism table.
Coincide the vertical cross wire with violet line and note down the reading. More the
telescope cross wire from one colour to other (starting with violet ending upto red)
and note down the corresponding xwindow & ywindow.
2. Remove prism. Bring the telescope in line with the collimator to have slit image onthe cross wire. Take xwindow & ywindow reading for direct ray.
3. The difference between direct reading and minimum deviation reading will give angleof minimum deviation of the prism (for the particular colour).
4. Plot the graph of angle of minimum deviation and wavelength known as calibrationcurve.
5. From the graph, find the value of the wavelength (R) of red of Hg source.6. Using the formula, calculate Ry.
Calculation
By analogy, wavelength of red light of Hg is equivalent to wavelength of red line ofhydrogen. In hydrogen spectrum red line is emitted when electron jumps from 2
ndto
3rd
orbit.
Using relation, 1/R = Ry(1/n121/n2
2) where, n1 = 2 & n2 = 3
Rydbergs constant can be found,
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Observation Table
Least count of spectrometer = 1 (one min.)
Direct reading X0 =
Y0 =
SourceColour
BandWavelength
Spectrometer Reading X-X0
deg
Y-Y0
deg
Mean
mX
(MSR+VSR)
Y
(MSR+VSR)
Hg
Violet 4162
Bluish
Violet4341
Blue 4861
Bluish
Green5240
Green 5400
Yellow 5893
Red
Graph is Wavelength R vs m
Result Rydbergs constant = ______ cm-1
Wavelength of red light = __________ from graph.
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WEDGE SHAPEDFILM
Aim To find the diameter of a wire using wedge-shaped film.
Apparatus Glass plate, wire, travelling microscope, sodium lamp assembly, lens.
Formula If a wedge-shaped film (transparent) is illuminated normally by a
monochromatic beam of light, alternate dark and bright fringes that are
straight, parallel, equidistant and also parallel to the edge of the wedge are
observed. The fringe width is given by.
tan =
=
where refractive index of the medium of the transparent film.
wedge angle.
wavelength of the monochromatic light.
The diameter d of the wire is given by d=L/2
L distance from the apex to the location of the wire.
Theory Refer to applied physics book.
Experimental Arrangement
Procedure
1. Place the converging lens in front of the extended monochromatic source at a distanceequal to the focal length of the lens ( 15 cm).
2. Arrange the glass plate using the stand inclined at an angle 450 to the light beam asshown in the figure.
3. The light is now made normally incident on the wedge-shaped air film (glass platesinclined to each other).
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4. Observe the fringe in the microscope. Find the fringe width considering the darkfringes.
5. Find length L (distance between the edge of the wedge and position of the wire) withthe travelling microscope.
6.
Calculate the diameter of the wire from the given formula.
Observation Table
TableI
Least count of the microscope = 0.001 cm.
Sr.No. No. of the
fringe
position (n)
Microscope ReadingDifference
????
= XnXn-2
2
Mean
MSR VSD TRXn
1 2nd
X2
2 4th
X4
3 6th
X6
4 8th
X8
5 10th
X10
6 12th
X12
TableII
Sr. No.
Microscope Reading at point
O.
Microscope Reading at point
A. L =
X0XA
Mean
LMSR VSD TR =
X0
MSR VSD TR =
XA
1
2
Calculations
The diameter d=L/2
Wavelength of the light used = 5893 A0
Refractive index of the air film = 1
Result Diameter of the given wire = ____________ cm.