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All INDIA SENIOR SCHOOL CERTIFICATE EXAMINATION - 2013-14

PHYSICS PROJECT

Refractive Indices with the helpof a hollow prism.

Project by:Madhur MehtaGrade : 12-A

Session :2013-14Board Rollno

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This is to certify that the bona fide work of the

student Madhur Mehta of class 12-A, Neerja Modi

School on the project titled Refractive Indices with

the help of a hollow prism. During the academicsession 2013-14.

. .

Date Rajneesh SinghPhysics Teacher)

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I would like to thank my Principal, Mrs Indu Dubeyand my Physics teacher Mr. Rajneesh Singh for

guiding and encouraging me to make this project.

Their support and words of enlightenment have

helped me a lot during the project.

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To investigate the dependence, of the angle of

deviation on the angle of incidence, using a hollow

prism filled one by one, with different transparent

fluids and find their respective refractive indices.

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Angle of Minimum DeviationDefinition : The minimum value of angle of deviation, is called angle

of minimum deviation.

Explanation : The figure is of a section of a prism ABC with AB and AC

as two refracting sides and BC as its base.

Let RQ be an incident ray.

QS be the refracted ray.

ST be the emergent ray.

Ang RQN1= i = angle of incidence.

Ang SQN3= r1= angle of refraction inside prism

Ang QSN3= r2= angle of incidence inside prism

Ang TSN2= e = angle of emergence

Ang BAC = A = angle of prism

Ang SFK = D = angle of deviation

In QFS, Ang KFS=Ang FQS + Ang FSQ

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D=(i - r1)+(e - r2) D=i + e (r1 + r2)

In QS1N3, r1 + r2 + AngQN3S =

The quadrilateral isAQN3S is a cyclic quadrilateral, then

A + AngQN3S = A = r1 + r2D = i + e - A

For the same value of deviation there are two values of angle of incidence.

One value is the value i and the other is the value e.

As the value of i increases, the value of e decreases and the angle ofdeviation decreases.

When the angle of deviation is minimum the value of i becomes equal to

the value of e.

The refracted ray QS goes parallel to base BC. Since i=e, we have r1 = r2

Hence at minimum deviation, when r1 = r2 = r (say).We have A = r1 + r2=2r or r = A/2

Also, at minimum deviation D=Dmand i=e

A+Dm = i+i = 2i or i=(A+Dm)/2

From Snells law:

n(Refractive Index) = (sin(i))/(sin(r))

=> n=[sin(A+Dm)/2]/sin(A/2)

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SNo. Contents Page No.

1. Aim 1

2. Theory 2

3. Materials Required 4

4.Working and Procedure

5

5. Observations 7

6. Calculations and Graphs 8

7.Result

9

8. Precautions and Sourcesof Error

10

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Drawing board, white sheets of paper, hollow

prism, different fluids (water, oil, glycerin),

drawing pins, pencil, half metre scale, thump pins,

graph papers and a protractor.

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1) Fix a white sheet of paper on a drawing board withthe help of thump pins.

2) Draw a straight line L and mark a point Q on it.3) Draw normal NQ through the point.4) Draw straight line RQ making an angle of with the

line NQ.

5) Put the prism with its refracting side AB on the lineL and mark the boundary of the prism.

6) Fill the prism with water.7)

Fix two or more office pins P1and P2vertically on

the line RQ. The distance between them should be at

least 10mm.

8) Look at the images of the pinsP1and P2through theface AC.

9) Bring one of your eye in line to the two images,keeping the other eye closed.

10) Fix two office pins P3and P4vertically, and 10cmapart so that the open eye sees all the four pins in one

straight line.

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11) Remove the pins P3and P4and encircle their prickson the paper.

12) Repeat the steps 4 to 11 with different angles of RQwith NQ.

13) Draw straight lines through points P3and P4to obtainemergent ray ST.

14) Produce ST inwards to meet the produced ray RQKat point F.

15) Measure the values of the angle KFS for differentangles of RQ with NQ to get different values of angle ofdeviation.

16) Measure angle BAC to get the value of angle ofprism A.

17) Repeat the same procedure for different fluids andrecord your observations.

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No. Angle of Incidence Angle of Deviation(WATER)

1. 30 27

2. 35 25

3. 40 24.5

4. 42 24

5. 45 23.56. 50 25

7. 55 26

No. Angle of Incidence Angle of Deviation

(GLYCERIN)

1. 35 382. 40 37

3. 45 35.5

4. 50 40

5. 55 41

No Angle of Incidence Angle of Deviation(OIL)

1. 30 40

2. 35 33

3. 40 35

4. 42 32

5. 45 39

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Plot the graphs between angle of incidence (i) and angle of

deviation (D) for each transparent fluid.

Refractive index of an object by Snells law is

n =[sin(A+Dm)/2]/sin(A/2)

Water: n = [sin(60+23.5)/2]/sin(60/2)

=0.6658/0.5 =1.3317

Glycerin: n=[sin(60+35.5)/2]/sin(60/2)

=0.7402/0.5 = 1.4804

Vegetable Oil: n=[sin(60+32)/2]/sin(60/2)

=0.7193/0.5=1.4386

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Water

From the graph the value of minimum deviation (Dm) =23.5.

The refractive index of water is =1.3317.

Glycerin

From the graph the value of minimum deviation (Dm) =35.5.

The refractive index of glycerin is =1.4804.

Vegetable Oil

From the graph the value of minimum deviation (Dm) =32.

The refractive index of vegetable oil is =1.4386.

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The angle of incidence should lie between 35=60.

The pins should be vertical.

Same angle of prism should be used for allobservations

Pin pricks may be thick.

Measurements of angles may be wrong.

Walls of glass prism may be thick.