physics manual sem1

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Applied Physics TSEC

1

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.


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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RYDBERGS CONSTANT

Aim To determine Rydbergs constant using calibration curve of Hg source.

Apparatus Spectrometer, prism, spirit level, mercury lamp, hydrogen tube.


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.



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.

physics manual sem1

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