CERTIFICATE
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
Teacher-in-charge
Mrs. Purnima Mehra
Kumar Jha
Signature of
Mr. Amarendra
(PGT)
Department of Physics
ACKNOWLEDGMENT
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.
PHYSICS
INVESTIGATORY
PROJECT
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.
Submitted by:-
Nisha Borah
Class: XII-B
Roll no. –
INTRODUCTION
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
“corpuscles” (particles) of light were fanned out
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.
APPARATUS:
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.
THEORY:
Refraction of Light through a Prism –
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 = r 1 + 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
equal.
The refracted ray QS goes parallel to base BC.
Since i = e, we have r1 = r2. (
∵ n=
sin i
sin r 1
=
sin e
sinr 2
)
Hence, at minimum deviation, when r1 = r2 =
r (say).
We have
A = r1 + r2 = r + r = 2r
⇒
A
2
r=
Also, at minimum deviation, D = Dm and i =
e
From relation,
We have,
A+D=i+e
A + Dm = i + i = 2i
⇒
i=
A+ Dm
2
From Snell’s law,
sin i
sin r
n=
A + Dm
2
A
sin
2
sin
We have
n=
This relation is useful for determination of n for
Prism material.
DIAGRAM:
DIAGRAM: Refraction through prism at
different angles
PROCEDURE:
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
on points Q1,Q2,Q3 and Q4.
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
AB.
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
and S4T4.
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.
OBSERVATIONS:
Angle of hollow prism A = 60⁰
S.No.
1
2
3
4
Angle
of
incidenc
e
40⁰
45⁰
50⁰
55⁰
Angle of
deviatio
n for
water
23⁰
24⁰
25⁰
26⁰
Angle
of
deviatio
n for
kerosen
e oil
36⁰
33⁰
34⁰
35⁰
Angle of
deviatio
n for
turpenti
ne oil
32⁰
33⁰
34⁰
35⁰
RESULTS:
 The angle of minimum deviation for –
Water Dm = 23⁰C
Kerosene oil Dm = 33⁰C
Turpentine oil Dm = 32⁰C
 The refractive indices of theWater n = 1.32
Kerosene oil n = 1.46
Turpentine oil n = 1.44
 Speed of light inWater v = 2.3x108 m/s
Kerosene oil v = 2.05x108 m/s
Turpentine oil v = 2.08x108 m/s
PRECAUTIONS:
 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.
SOURCES OF ERRORS:
 Pin pricks may be thick.
 Measurement of angles may be wrong.
BIBLIOGrAPHY
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
CONTENTS
 Introduction
 Experimental setup
 Bibliography
CONTENTS
 Introduction
 Experimental setup
 Bibliography