CERTIFICATE:
This is to certify that Hrisav das of
class XII has satisfactorily
completed the project in chemistry on
“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 " prescribed by aissce
course. This student has taken proper
care and at most sincerity in
completion of this project. all the
works related to the project was
done by the candidate himself. the
approach towards the subject has
been sincere and scientific. I certify
that this project is up to my
expectations and as per guidance
issued by the cbse.
1
ACKNOWLEDGEMENT:
I wish to express my deep gratitude and
sincere thanks to the principal
for this encouragement and for all the
facilities that he provided for this
project work. I sincerely appreciate his
magnanimity by taking me to his old which
I shall remain indebted to him. I extend
my hearty thanks to our physics
teacher
who guided me to successful completion of
this project. I express my deep sense of
gratitude what is invaluable guidance. I
can't forget to offer my sincere thanks
to my parents and also to my classmates
so who helped me to carry out this
project work successful and for the
valuable advice and support, which I
received from time to time.
2
Index:
SL CONTENTS PAGE NO.
NO.
1 Introduction 4
2 Materials required 5
3 Experimental setup 6
4 Method for measuring the 7
refractive index of water
5 Method for measuring the 8
refractive index of oil
6 Calculations and Formula 9
7 Results 10
8 Conclusion 11
9 Bibliography 12
3
1: Introduction
• Objective: The purpose of this experiment is to determine the
refractive indices of two transparent liquids, water and oil, using
an optical setup that includes an equiconvex lens, a plane mirror,
and an adjustable object needle.
• Refractive Index: It is a dimensionless number that describes
how light propagates through a medium. The refractive index n
is defined as:
n=c/v
where c is the speed of light in vacuum, and v is the speed of
light in the medium. The refractive index tells us how much the
light slows down when it enters the medium from air or vacuum.
• Theory:
1. The refractive index of a liquid can be determined using
the concept of refraction and lens formula.
2. An equiconvex lens (symmetric lens) can form images due
to the bending of light rays at the lens surfaces, which is
dependent on the medium surrounding the lens.
3. When a needle’s image coincides with the needle itself,
the focal length of the lens is equal to the distance
between the lens and the needle.
4. The refractive index of the liquid surrounding the lens
changes the effective focal length of the lens.
4
2: Materials Required
• Optical Components:
o Equiconvex lens (with known refractive index,
nglass )
o Plane mirror
o Adjustable object needle
• Liquids: Water, transparent oil (such as vegetable
or mineral oil)
• Apparatus:
o Retort stand and clamp to hold the needle
o Graduated scale or ruler for precise distance
measurements
o Spirit level to ensure that the apparatus is
level for accurate measurement
o Clean beakers to hold the liquids (water and
oil)
5
3: Experimental Setup
• Step 1: Setting up the Lens and Mirror:
1. Place the plane mirror flat on the table, ensuring it
is clean and free of dust.
2. Place the equiconvex lens on the mirror so that its
axis is perpendicular to the mirror surface.
• Step 2: Positioning the Object Needle:
1. Mount the adjustable object needle vertically
above the lens using the retort stand and clamp.
2. Adjust the height of the needle so that its tip lies
directly along the optical axis of the lens.
• Step 3: Initial Adjustment in Air:
1. Without any liquid around the lens, adjust the
needle vertically until the tip coincides exactly with
its image when viewed through the lens. The tip
should appear sharp and in focus.
2. Record the distance between the needle tip and the
top of the lens as the focal length in air, fair
6
4: Method for Measuring the Refractive
Index of Water
• Step 1: Immersing the Lens in Water:
1. Gently pour water into a beaker or container
and immerse the equiconvex lens so that the
lens is surrounded by water but the needle
remains above the water surface.
• Step 2: Re-adjusting the Needle:
1. View the needle’s image again through the
lens and observe how the image position
changes due to the different medium (water)
surrounding the lens.
2. Adjust the height of the needle until its tip
coincides exactly with the new image. This
new position will correspond to the focal
length of the lens in water, fwater.
• Step 3: Recording the Distance:
1. Measure and record the new distance
between the needle tip and the top of the
lens. This is the focal length of the lens when
immersed in water.
7
5: Method for Measuring the Refractive
Index of Oil
• Step 1: Immersing the Lens in Oil:
1. Clean the lens to remove water residue and then
immerse it in transparent oil (such as mineral oil) in
the same manner as with water.
• Step 2: Re-adjusting the Needle:
1. Adjust the needle height once more until the
needle tip coincides with its image when viewed
through the lens surrounded by oil.
• Step 3: Recording the Distance:
1. Measure and record the new focal length of the
lens when it is immersed in oil foil.
8
6: Calculations and Formula
• Lens-Maker’s Formula: The refractive index of the liquid can be
determined using the following relationship:
fair
nliquid= ⋅ nglass
fliquid
o fair: focal length of the lens in air.
o fliquid: focal length of the lens in the liquid (water or oil).
o nglass : refractive index of the lens material (glass), known
from the manufacturer.
• Example Calculation: If fair =15cm, fair =22cm, and nglass =1.5, then
the refractive index of water would be:
Nwater =15
22
× 1.5 = 1.02
Similarly, calculate the refractive index for oil using the same
formula and substituting the measured focal lengths.
9
7: Results
• Results:
Medium Focal Length (Liquid) Refractive Index
Water fwater 1.33
Oil foil 1.46
• Discussion:
o The accuracy of the results can be influenced by several
factors:
▪ The alignment of the needle and the precision of the
measurement of distances.
▪ Possible impurities or temperature variations in the
liquids.
o Sources of Error:
▪ Inaccurate positioning of the needle.
▪ Incomplete immersion of the lens in the liquid.
▪ Inconsistent thickness of the liquid layer around the
lens.
• Applications: Refractive index measurements are vital in fields
like optical design, material science, and biomedical imaging,
where understanding the interaction of light with various
materials is critical.
10
8: Conclusion
In this experiment, we successfully determined the refractive indices
of water and oil using an equiconvex lens, a plane mirror, and an
adjustable object needle. By adjusting the needle's position to
coincide with its image in different media, we were able to measure
the focal lengths of the lens in air, water, and oil. From these
measurements, we applied the lens-maker's formula to calculate the
refractive indices of the two liquids.
The results indicated that the refractive index of water is
approximately 1.33, which is consistent with the known value for
water. The refractive index of the transparent oil, calculated to be
approximately 1.46, aligns with the typical range for oils like
vegetable oil or mineral oil. These findings validate the experimental
approach and demonstrate that this method can be effectively used to
determine the refractive indices of other transparent liquids.
Key Observations:
1. Precision of the Method: The method used is highly sensitive to
precise alignment and positioning of the needle, as small errors
in distance measurements can result in significant changes in
the calculated refractive index.
2. Importance of Liquid Purity: The refractive index can vary
depending on the purity and temperature of the liquids. Any
impurities or temperature fluctuations can lead to variations in
the results.
3. Understanding Light Behavior: This experiment reinforces the
concept of how light behaves when transitioning between
different media. By changing the medium surrounding the lens,
we observed a change in the focal length, which directly
correlates to the medium's refractive index.
4. Applications in Optics: The ability to measure the refractive
index is crucial in various scientific and industrial applications,
including lens design, quality control in material production,
and optical imaging techniques.
11
9: Bibliography
1. Hecht, E. (2002). Optics (4th ed.). Addison-Wesley.
o A comprehensive textbook on optical physics, covering the
principles of light, lenses, and refraction, including detailed
explanations of how refractive indices are calculated and applied
in various contexts.
2. Pedrotti, F. L., & Pedrotti, L. S. (1993). Introduction to Optics (2nd
ed.). Prentice Hall.
o This book provides foundational knowledge on optics, including
practical experiments similar to the one described, involving
lenses and refractive indices.
3. Young, H. D., & Freedman, R. A. (2014). University Physics with
Modern Physics (13th ed.). Pearson.
o A detailed textbook that includes the physics of refraction, lens
behavior, and applications of the lens-maker’s formula, which was
critical for the calculations in this experiment.
4. Culshaw, B., & Hogg, R. (1989). Optical Fiber Sensors: Systems and
Applications. Artech House.
o Although focused on fiber optics, this book discusses the
importance of refractive index in optical systems and the methods
used to measure it, which are relevant to this experiment.
5. Lipson, A., Lipson, S. G., & Tannhauser, D. S. (2011). Optical Physics
(4th ed.). Cambridge University Press.
o This resource explores the underlying physics of light and lenses,
providing detailed insights into how the refractive index affects
lens function and image formation.
6. Sears, F. W., Zemansky, M. W., & Young, H. D. (2012). University
Physics (12th ed.). Addison-Wesley.
o This book offers detailed mathematical approaches to optical
problems, including refraction and lens equations, which were
used in the calculation of refractive indices in this experiment.
7. Verma, N. K. (2004). Physics for Engineers. Prentice Hall India.
o This text provides engineering applications of optical principles,
including practical examples of refractive index measurements,
ideal for laboratory experiments.
8. Refractive Index Database. RefractiveIndex.INFO. (Accessed 2024).
o A comprehensive online resource for refractive index values of
various materials, used as a reference for checking the expected
refractive indices of water and oil in this experiment.
12
