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Physics Investigatory Project


Academic year: 2021

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This is to certify that Nisha Borah of class XII-B

of science of Roll no. ……… of Army

Public School Basistha has successfully completed and submitted investigatory project entitled “To investigate the dependence, of the angle of

deviation on the angle of incidence, using a hallow prism filled, one by one, with different transparent fluids” to the department of physics for AISSCE practical examination 2015-2016 as set by Central Board of Secondary Education and it wholly fulfilled the standard set by Central Board of Secondary Education.

This project is absolutely genuine and does not indulge any kind of plagiarism.

The reference taken in making this project has been declared at the end of this project.

Signature of Principal Signature of

Teacher-in-charge Mrs. Purnima Mehra Mr. Amarendra Kumar Jha


(PGT) Department of Physics


It is my proud privilege to offer my sincere thanks to the Central Board of Secondary

Education who has given me this opportunity to make a project on this subject successfully.

I would like to offer my sincere thanks and gratitude to Madam Purnima Mehra, the principal of my school to complete this in time.

I am extremely indebted to our physics teacher Mr. Amarendra Kumar Jha for his able guidance, timely help and constructive

encouragements towards the completion of this project.

And at last, I would like to offer my sincere thanks to our lab assistance for guiding me on a step by step basis and ensuring that I completed all my experiments with ease.





TOPIC: 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.

Submitted to the department of physics, Army Public

School Basistha for the fulfillment of AISSCE - 2015-2016, SCIENCE.


Nisha Borah Class: XII-B Roll no. –


In optics, a prism is a transparent optical

element with flat, polished surfaces that refracts light. The exact angles between the surfaces

depend on the application. The traditional

geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in

colloquial use “prism” usually refers to this type. Some types of optical prism are not in fact in the shape of geometric prisms. Prisms can be made from any material that is transparent to the

wavelengths for which they are designed. Typical materials include glass, plastic and fluorite. Prism can be used to break light up into its constituent spectral colors (the colors of the rainbow). Prisms can also be used to reflect light, or to split light into components with different polarizations.

Before Isaac Newton, it was believed that white light was colorless, and that the prism itself produced the color. Newton’s experiments

demonstrated that all the colors already existed in the light in a heterogeneous fashion, and that


because particles with different colors traveled

with different speeds through the prism. It was only later that Young and Fresnel combined Newton’s particle theory with Huygens’ wave theory to show that color is the visible manifestation of light’s

wavelength. Newton arrived at his conclusion by passing the red color from one prism through

second prism and found the color unchanged. From this, he concluded that the colors must already be present in the incoming light and white light

consists of a collection of colors. As the white light passes through the triangular prism, the light

separates into the collection of colors: red, orange, yellow, green, blue, indigo and violet. This

collection of colors formed by the prism is called the spectrum. The separation of white light into its spectrum is known as dispersion.

Dispersion occurs because each color travels through the prism at different speeds. Violet travels the slowest through the prism; hence we can see it refracting the most. On the other hand, red passes through at a much fast rate which makes its angle of refraction less, hence red is too scarce to be seen.


Experimental setup

AIM: To investigate the dependence, of the angle

of deviation on the angle of incidence, using a hallow prism filled, one by one, with different transparent fluids.


Drawing board, white sheets of paper, hollow prism, different liquids (water, kerosene oil, etc), drawing pins, pencil, half meter scale, thump pins, graph papers and a protractor.



Diagram shows section ABC of a prism taken by a vertical plane, perpendicular to the edge. BC is the base of the prism and AB and AC are its two

refracting surfaces.

DIAGRAM: Refraction through a prism. RQ is the incident ray.

QS is the refracted ray. ST is the emergent ray.

RQN1 = i = angle of incidence

SQN3 = r1 = angle of refraction inside prism

QSN3 = r2 = angle of incidence inside prism

TSN2 = e = angle of emergence

BAC = A = angle of prism SFK = D = angle of deviation In QFS, KFS = FQS + FSQ D = (i – r1) + (e – r2)


D = i + e – (r1 + r2)

… (1)

In QS1N3, r1 + r2 + QN3S = 180⁰

… (2)

The quadrilateral AQN3S is cyclic quadrilateral, then

A + QN3S = 180 … (3) From (2) and (3) A = r1 + r2 … (4) Eq. (1) become D = i + e - A D + A = i + e … (5)

Angle of Minimum Deviation

- Definition: The minimum value of angle of

deviation is called angle of minimum deviation. It is represented by the symbol Dm.

 Explanation: For same angle of deviation (D) there are two values of angle of incidence. One value equals ‘i’ and other value equals ‘e’.

As angle ‘i’ is increased from a small value, ‘e’ decreases from large value and angle of

deviation decreases. When angle of deviation is minimum (Dm), then, ‘i’ and ‘e’ becomes


The refracted ray QS goes parallel to base BC. Since i = e, we have r1 = r2. ( ∵ n= sin isin r1 =

sin e sinr2 )

Hence, at minimum deviation, when r1 = r2 =

r (say).

We have A = r1 + r2 = r + r = 2r

r = A2

Also, at minimum deviation, D = Dm and i =


From relation, A + D = i + e

We have, A + Dm = i + i = 2i

i = A+ D2 m From Snell’s law,

n = sin isin r We have n = sinA + Dm 2 sinA 2

This relation is useful for determination of


for Prism material.



DIAGRAM: Refraction through prism at different angles


1.A white sheet of paper was fixed on the

drawing board with the help of drawing pins. 2.A straight line XX’ parallel to the length of the

paper was drawn nearly in the middle of the paper.

3.Points Q1,Q2,Q3 and Q4 were marked on the

straight line XX’ at suitable distances of about 6cm.

4.Normal’s N1Q1,N2Q2,N3Q3 and N4Q4 were drawn


5.Straight lines R1Q1,R2Q2,R3Q3 and R4Q4 were

drawn making angles of 40⁰,45⁰,50⁰ and 55⁰ respectively with the normals.

6.One corner of the prism was marked as A and it was taken as the edge of the prism for all the observations.

7.Prism with its refracting face AB was put in the line XX’ and point Q1 was put in the middle of


8.The boundary of the prism was marked.

9.Two pins P1 and P2 were fixed vertically on the

line R1Q1 and the distance between the pins

were about 2cm.

10. The images of points P1 and P2 were looked

through face AC.

11. Left eye was closed and right eye was

opened and was brought in line with the two images.

12. Two pins P3 and P4 were fixed vertically at

about 2cm apart such that the open right eye sees pins P4 and P3 as images of P2 and P1 in

one straight line.

13. Pins P1,P2,P3 and P4 were removed and their

pricks on the paper were encircled.

14. Steps 7 to 13 were again repeated with points Q2,Q3 and Q4 for i=45⁰,50⁰ and 55⁰.

15. Straight lines through points P4 and P3 were

drawn to obtain emergent rays S1T1, S2T2, S3T3


16. T1S1,T2S2 ,T3S3 and T4S4 were produced inward

in the boundary of the prism to meet produced incident rays R1Q1, R2Q2,R3Q3 and R4Q4 at points

F1,F2,F3 and F4.

17. Angles K1F1S1,K2F2S2,K3F3S3 and K4F4S4 were

measured. These angles give angle of deviation D1, D2,D3 and D4.

18. Values of these angles were written on the paper.

19. Angle BAC was measured in the boundary of the prism. This gives angle A.

20. Observations were recorded.


Angle of hollow prism A = 60⁰ S.No. Angle of incidenc e Angle of deviatio n for water Angle of deviatio n for kerosen e oil Angle of deviatio n for turpenti ne oil 1 40⁰ 23⁰ 36⁰ 32⁰ 2 45⁰ 24⁰ 33⁰ 33⁰ 3 50⁰ 25⁰ 34⁰ 34⁰ 4 55⁰ 26⁰ 35⁰ 35⁰



 The angle of minimum deviation for –

Water Dm = 23⁰C

Kerosene oil Dm = 33⁰C

Turpentine oil Dm = 32⁰C

 The refractive indices of Water n = 1.32

Kerosene oil n = 1.46 Turpentine oil n = 1.44  Speed of light

Water v = 2.3x108 m/s

Kerosene oil v = 2.05x108 m/s

Turpentine oil v = 2.08x108 m/s


 The angle of incidence should lie between 35⁰ – 60⁰.

 The pins should be fixed vertical.

 The distance between the two pins should not be less than 10mm.

 Arrow heads should be marked to represent the incident and emergent rays.


 The same angle of prism should be used for all the observations.


 Pin pricks may be thick.

 Measurement of angles may be wrong.


The following sources were used for the

appropriate information required to complete the project:

 Comprehensive: Practical Physics Class XII  NCERT textbook of class XII

 Google



Experimental setup





Experimental setup


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