PHYSICS INVESTIGATORY PROJECT
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
GROUP MEMBERS:
MADHUMITHA.R
VEDHAA SHREE.D
HARSHINI.R.R
HARINI.N
JANANI.K
CONTENTS
• Introduction
• Experimental setup
• Procedure
• Observations
• Results
• Precautions
• Sources of errors
• Bibliography
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• 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.
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• 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.
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• 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.
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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
•
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DIAGRAM: Refraction 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.
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• 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
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D = (i – r1) + (e – r2)
D = i + e – (r1 + r2) … (1)
QS1N3, r1 + r2 +
QN3S = 180⁰ … (2)
uadrilateral AQN3S is cyclic quadrilateral, then
A + QN3S = 180 … (3)
From (2) and (3)
A = r1 + r2 … (4)
(1) become
D = i + e - A D + A = i + e … (5)
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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.
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• The refracted ray QS goes parallel to base BC.
• Since i = e, we have r1 = r2. (
∵ n=
sin i =
sin r
1
sin e
sin r
2
)
• Hence, at minimum deviation, when r1 = r2 = r (say).
• We have
A = r1 + r2 = r + r = 2r
•
⇒
r=
A/2
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• Also, at minimum deviation, D = Dm and i = e
• From relation, A + D = i + e
• We have,
A + Dm = i + i = 2i
•
• From Snell’s law,
n = sin i /sin r
• We have
⇒
i = A+ D
/2
n=
•
sin A +
Dm/
2
• sin A2
• This relation is useful for determination of n for Prism material.
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DIAGRAM
Refraction through prism at different angles
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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.
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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.
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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.
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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.
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OBSERVATIONS
S.No.
Angle of incidencee
Angle of
deviation for
water
Angle of deviation
for kerosene oil
Angle of
deviation for
turpentine oil
1
40⁰
23⁰
36⁰
32⁰
2
45⁰
24⁰
33⁰
33⁰
3
50⁰
25⁰
34⁰
34⁰
4
55⁰
26⁰
35⁰
35⁰
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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
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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.
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SOURCES OF ERRORS
• Pin pricks may be thick.
• Measurement of angles may be wrong.
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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
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