HEM SHEELA
MODEL SCHOOL
DURGAPUR
IN PARTIAL FULFILLMENT OF AISSCE - 2025
NAME OF THE : DEEPTANSHU
AYUSH MONI
STUDENT SINHA
BOARD ROLL NUMBER :
CLASS : XII XII
SESSION : 2024-2025
2025-2026
1
PHYSICS
PROJECT
TOPIC :
To find the refractive indices of (a)
water (b) oil (transparent) using a
plane mirror , an equiconvex lens
(made from a glass of known
refractive index) and an adjustable
object needle.
2
ACKNOWLEDGEMENT
I would like to express my special thanks to our
Principal madam Miss.Anindita Home
Choudhury, who gave me the golden
opportunity to do this wonderful project which
also helped me to do a lot of research and I came
to know about so many new things.
The completion of this undertaking could have
not been possible without the assistance of
Dr. Goutam Chakraborty sir. I extend my
gratefulness and thank our lab assistant sir Mr.
Sanjib Banerjee who always made our practical
classes hassle free with his constant presence of
mind and helpful attitude.
I take this opportunity to thank my parents who
helped me a lot in finalizing this project with
resources and lots of motivation.
Signature of student:
3
TEACHER’S CERTIFICATE
This is to certify that Deeptanshu Sinha of
This XII
class of Hem
is to certify thatSheela
Ayush Model
Ayush Moni
Moni of School
class XII has
of
Hem Sheela
completed the Model
assignedSchool has project
Physics completed the
himself
assigned
and underPhysics project himself
my guidance. He hasand under and
prepared my
guidance. He
submitted the has prepared
project and submitted
by following the
guidelines
project
and by following
instructions guidelines
given by theand instructions
teachers and
given by
within the teachers
speculated timeand within speculated time
of submission.
of submission.
_____________ ________________
SIGNATURE OF SIGNATURE OF
INTERNALEXAMINER
INTERNAL EXTERNAL
EXAMINER EXAMINER
____________
_____________________
SIGNATURE OF PRINCIPAL
4
INDEX
SL. NO. TOPIC PAGE
1 Acknowledgement 3
2 Teacher’s 4
Certificate
3 Index 5
4 Introduction 6
5 Aim/ objective 7
6 Materials Required 7
7 Diagram 8
8 Theory 9-10
9 Procedure 11-12
10 Observations 13-14
11 Calculations 14-15
12 Results 15
13 Precautions 16
14 Sources of errors 16
15 17
Bibliography
5
INTRODUCTION
In optics, the refractive index (a.k.a. refraction
index) of an optical medium is a dimensionless
number that indicates the light-bending ability of
that medium. The refractive index determines how
much the path of light is bent, or refracted when
entering a material. This is described by
Snell's law of refraction :-
n₁Sinθ₁ = n2Sinθ2 , Where,
θ₁ = Angles of incidence
θ2 = Angle of refraction,
Respectively of a ray crossing the interface
between two media with refractive indices n₁ and n₂
6
OBJECTIVE
To find the refractive index of water, oil using a
plane mirror and an equiconvex lens and an
adjustable object needle.
MATERIALS REqUIRED
Convex lens
Plane mirror
Water
Oil
Clamp stand
An Optical needle
Plumb line
Knitting needle
Half meter Scale
Glass slab
Spherometer
7
DIAGRAMS
8
THEORY
9
10
PROCEDURE
(a) For focal length of convex lens:
1. Find the rough focal length of the convex lens.
2. Place a plane mirror on the horizontal base of the iron
stand and then a convex lens on the plane mirror.
3. Hold the needle in the clamp stand and adjust its
position on the stand such that there is no parallax
between tip of the needle and its image.
4. Measure distance between tip and upper surface of
the lens by using a plumb line and half meter scale. Also
measure the distance between tip of needle and upper
surface of the mirror. Take the mean of the two
readings. This means distance will be equal to the focal
length of the convex lens (fi).
(b) For focal length of the combination.
5. Put a few drops of the water on the plane mirror and
put the convex lens over it with its same face above as
before. The water spreads in a form of layer and acts
like a Plano-concave lens.
6. Repeat the steps 3 and 4 to determine the equivalent
focal length of the combination.
11
7. Record the observation.
8. Repeat the steps 5, 6, 7 for other transparent liquid
(oil).
(c) For radius of curvature of convex lens surface:
9. Determine the pitch and the least count of the
spherometer.
10. Remove the convex lens and dry it completely. Put
the spherometer on this lens surface.
11. All the three legs of the spherometer should be
placed symmetrically on the lens and adjust the central
screw tip to touch the surface of the lens.
12. Remove the spherometer from the surface of the
lens and place on the plane mirror surface and record
the reading.
13. Repeat the steps 10 and 11 three times.
14. Obtain the impressions of the three legs of the
spherometer on a paper and mark them and their
average distance.
𝑙1+𝑙2+𝑙3
l= 3
12
OBSERVATIONS
Pitch of the spherometer = 1 cm
Least count of the spherometer = 0.01 cm
Distance between the legs :
(1) AB = 3cm
(2) BC = 3cm
(3) CA = 3cm
13
CALCULATIONS
14
RESULTS
The refractive index of water (μ1) = 1.0831
The refractive index of oil (μ2) = 1.2886
15
PRECAUTIONS
1. The plane mirror should be clean and fully shining surface.
2. The liquid taken should be transparent.
3. The parallax should be removed tip to tip.
4. The eye should be at a distance about 30 cm from the needle
while removing the parallax.
5. Only few drops of liquid should be taken so that its layer
should be thick.
6. The legs of the spherometer should be vertical.
7. The centre leg of the spherometer should turn in one
direction only.
SOURCES OF ERROR
1. Liquid may not be quite transparent.
2. The parallax may not be fully removed.
3. The spherometer legs should be placed symmetrical on the
surface of the convex lens.
4. The tip of the central screw should not just touch the surface
of lens or mirror.
16
BIBLIOGRAPHY
NCERT PHYSICS TEXTBOOK
NCERT PHYSICS LAB MANUAL
www.google.com
www.byjus.com
www.scribd.com
www.wikipedia.com
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