uday phy gd

8/13/2019 uday phy gd

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Submitted by-Sidharth sharma

Uday pratap

Vaibhav kaushal

Vikashdeep sagar


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IntroductionRelated theoryObjectiveImportant terms

Formula usedDescription of apparatusProceduresMeasurements

ObservationsResultsPrecautions

CONTENTS


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INTRODUCTION Sodium lights actually energize

the sodium gas trapped insidethe bulb to produce the light.

Wavelength is the distancebetween peaks (high points).

This is similar to Youngs

experiment.


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RELATED THEORY

The wave nature of light was established in the early part ofthe 19th century.

Fresnels experiment with the Biprism was one of the earliest

experiments to yield values for the wavelength of light. To make two coherent source for interference .Biprism make

two sources.

It is similar to Youngs Double slit experiment .


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IMPORTANT TERMS

FresnelsBiprismYoungs

Double SlitExperiment

Interferenceof light Diffraction


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FRESNEL BIPRISM

Fresnel used a biprism to showthe phenomenon of interference.

A biprism is essentially a

combination of two acute prismplaced base to base.

A prism whose refracting angle

is very nearly 180 degrees. to determine wavelengths and

interference fringes


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Youngs Double SlitExperiment In the early 1800's (1801 to 1805), Thomas

Young conducted an experiment. He allowed

light to pass through a slit in a barrier so it

expanded out in wave fronts from that slit as a

light source.

That light, in turn, passed through a pair of slits

in another barrier (carefully placed the right

distance from the original slit). Each slit, in turn,

diffracted the light as if they were also individual

sources of light. The light impacted an

observation screen.


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When a single slit was open, it merelyimpacted the observation screen with

greater intensity at the center and thenfaded as you moved away from the center.There are two possible results of thisexperiment:

Particle interpretation: If light exists asparticles, the intensity of both slits will bethe sum of the intensity from the individualslits.

Wave interpretation: If light exists as waves,

the light waves will have interference underthe principle of superposition, creatingbands of light (constructive interference)and dark (destructive interference).

CONTD


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Interference of light

When two light waves from different coherent

sources meet together, then the distribution of

energy due to one wave is disturbed by the

other. This modification in the distribution oflight energy due to super position of two light

waves is called "Interference of light".

Two types----- constructive interference

destructive interference

----The point at which intensity of light is

maximum is called constructive interference.

-----The point at which intensity of light is

minimum is called destructive interference.

INTERFERENCE CONDITIONS-----

Light must be monochromatic, i.e., involve just

Lamps, flashlights, etc all produce light. But this light is released in many directions, and

the light is very weak and diffuse. In coherent light the wavelength and frequency of the

photons emitted are the same. The amplitude may vary. Such things as lasers and

holograms are composed of coherent light.


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Diffraction

Diffraction is a phenomenon done by

visible light when it passes through a

prism it is seen that it spreads into seven

different colored lights. When it rains arainbow is visible because a drop of rain

acts as the prism and 7 different bright

lights are seen as per the difference in

their wavelengths. More examples can be

light falling on CD or a DVD which enables

us to see different colors. When we blowsoap bubbles against the light, it is notseen as white but as blue, pink, red, etc.


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- The wavelength of the sodium light is given by the

formula in case of biprism

experiment.

= 2d / D

Where = fringe width,

2d = distance between the two virtual sources,

D = distance between the slit and screen.

Again 2d = d1d2Where d1 = distance between the two images formed by

the convex lens in one position.

d2 = distance between the two images formed by the

convex lens in the second position.

Used formula


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Description of

apparatus


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CONTD


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CONTD


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CONTD


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CONTD


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CONTD


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CONTD


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Procedure1. Mount the gadgets on the optical bench.

2.Study all the movements on each stand.3. Ensure that all the pieces are aligned at roughly the same height

4. Remove the stand with the convex lens from the optical bench.

5. Bring the eyepiece close to the biprism.

6. Looking through the eyepiece you will see a bright vertical patch of light. A

slight rotation of the biprism in its own plane will break up this patch into

vertical equidistance fringes.

7. Adjust the slit width to get the best compromise between brightness and

sharpness of the fringe pattern.

8. Move the eyepiece slowly away from the biprism along the optical bench

to a

distance of about 100 cms. Keeping the fringe pattern all the time in the field

of view.9. Keeping eyepiece at a distance of 100 cm from the biprism, measure the

fringe

width by measuring the distance traversed by the eyepiece in crossing about

10 fringes using the main and circular scales on the eye-piece.

10. Interpose the convex lens between the biprism and the eyepiece making

sure

that D>4f.

11. Move the lens along the optical bench till you locate two conjugate

positions

of the lens at which you can see real images of the double slit in the field of

view of the eyepiece.

12. Without disturbing the positions of the slit, biprism and the eyepiece

measure

the double-slit image separations d1 and d2.


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MeasurementsMeasurement of : (Fringe width)

1. The eyepiece is fixed about 100cm away from the slit.

2. The vertical crosswire is set on one of the bright fringes and the

reading on the eyepiece scale is noted.

3. The crosswire is moved on the next bright fringe and the

reading is noted. In this way observation are taken for about 20

fringes.

Measurement of D: (distance between source and screen)

1. The distance between the slit and eyepiece gives D.

Measurement of 2d: (distance between the two sources on

screen)

1. For this part the distance between the eyepiece and slit should

be kept slightly more than four times the focal length of lens. If

necessary the position of the slit and the biprism should not be

altered.

2. The convex lens is introduced the biprism and eyepiece and is

placed near to the eyepiece. The lens is moved towards thebiprism till two sharp images of the slit are seen. The distance d1

is measured by the micrometer eyepiece.

3. The lens is moved towards the biprism till two images are again

seen the distance between these two images give d2.

4. At least two sets of observation for d1 and d2 are taken.


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ObservationFor fringe width--No. of division on the vernire scale-

Least count of vernire-

No. of

fringeMicrometerreading(a) No. of

fringe

Micrometerreading(a) Difference

For 10 fringeMean for10 fringe

Fringewidth(mm)

[Mean10]

MS VS Total(mm)

MS VS Total(mm)

12

3

4

5

67

8

9

10

1112

13

14

15

1617

18

19

20


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CONTDMeasurement of D:

Position of the slit a) =cmPosition of the eyepiece b)=.cmObservation value of D b-a)=..cm


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CONTDMeasurement of 2d-

Micrometer Reading

Mean 2dObservation of d1 Observation of d2

tion of Image Position of IIImage

Position of I Image Position of II Image

VS Total MS VS Total MS VS Total MS VS Total


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Results

Wavelength of Sodium light=

Standard Value of wavelength=5893A0


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Precautionsi) The setting of uprights at the same

level is essential

ii) The Slit should be vertical andnarrow.

iii) Fringe shift should be removed

iv) Bench error should be taken into

account.

v) Crosswire should be fixed in the

center of the fringe while taking observationsfor fringe width.

vi) The micrometer screw should be

rotated only in one direction to avoid backlash

error.

vii) The fringe width should be measured

at a fairly large distance.viii) Convex lens of shorter focal length

should be used (f=25 cms. Approx)

ix) Motion of eyepiece should be

perpendicular to the lengths of the bench.


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