2016
A PROJECT REPORT ON
Experiment to find refractive index of liquid using
Convex lens and plane mirror
Submitted to:
Mr.Praveen Arya
Submitted by: Ayush
Kumar Sharma
I would like to thank all the staff of my school for
providing adequate details and date to give a shape
of this report, their valuable support and advice, and
for giving knowledge in each and every section.
I am also thankful to Mr. Praveen Arya under whose
support we have been able to make this project
report a great success.
Ayush Kumar Sharma
XII B
This Project Report has been Satisfactory
made by Ayush Kumar Sharma Of class XII
B and submitted to Maharishi Vidya Mandir
-1
Preface
Introduction
Experiment
1)Objective
2)Apparatus
3)Theory
4)Procedure
5)Observations and calculations
6)Precautions and Sources Of Error
Bibliography
PREFACE
In this article, we are trying to help CBSE board class
12th student with their CBSE board 12th project. In
this project, Students are required to establish project
of “To find Refractive index of liquids using convex
lens and plane mirror” and make CBSE board class
12th physics school project work.
Introduction:
Refraction of Light
Refraction is the bending of a wave when it enters a medium
where its speed is different. The refraction of light when it
passes from a fast medium to a slow medium bends the light ray
toward the normal to the boundary between the two media. The
amount of bending depends on the indices of refraction of the
two media and is described quantitatively by Snell's Law.
Refraction is
responsible for
image formation
by lenses and
the eye.
As the speed of light is reduced in the slower medium, the wavelength is
shortened proportionately. The frequency is unchanged; it is a
characteristic of the source of the light and unaffected by medium
changes.
Index of Refraction
The index of refraction is defined as the speed of light in vacuum
divided by the speed of light in the medium.
The indices of refraction of some common substances are given below
with a more complete description of the indices for optical glasses given
elsewhere. The values given are approximate and do not account for the
small variation of index with light wavelength which is
called dispersion.
Material
n
Material
n
Vacuum
1.000
Ethyl alcohol
1.362
Air
1.000277
Glycerine
1.473
Water
4/3
Ice
1.31
Carbon disulfide
1.63
Polystyrene
1.59
Methylene iodide
1.74
Crown glass 1.50-1.62
Diamond
2.417
Flint glass 1.57-1.75
Snell's Law
Snell's Law relates the indices of refraction n of the two media to the
directions of propagation in terms of the angles to the normal. Snell's
law can be derived from Fermat's Principle or from the Fresnel
Equations.
If the incident medium has the larger index of refraction, then the angle
with the normal is increased by refraction. The larger index medium is
commonly called the "internal" medium, since air with n=1 is usually
the surrounding or "external" medium. You can calculate the condition
for total internal reflection by setting the refracted angle = 90° and
calculating the incident angle. Since you can't refract the light by more
than 90°, all of it will reflect for angles of incidence greater than the
angle which gives refraction at 90°.
Fermat's Principle and Refraction
Fermat's Principle: Light follows the path of least time. Snell's Law can
be derived from this by setting the derivative of the time =0. We make
use of the index of refraction, defined as n=c/v.
Objective:Determine the refractive index of a liquid.
Apparatus:Convex lens, liquid, plane mirror, retort stand with clamp
and pin,
spherometer, meter rule.
Theory:A spherometer: is an instrument for the precise
measurement of
the radius of a sphere. This experiment is one of the most
important
experiments to find the refractive index for all the liquids.
As we know
that the light pass in vacuum with constant speed which is
equal to
(300000 Km/Sec) and the light pass also in different
material
which is transparent like (Air, water, glass) because the
atoms of this
material has ability to absorb the light and retransmission
and dispersion
it, for this reason the light pass through different materials
in different
speeds less than its speed in vacuum. The speed of light
depend on the nature of material, for that reason when
the light pass from one medium to another, a change in
speed will occur
and change in direction happened, this phenomena called
refraction, and
controlled by "Snell's law of refraction "and to explain the
change in
light speed when it pass from vacuum to certain medium,
we used a
physical quantity called refractive index or index of
refraction of
material (n) is the ratio of the light speed in vacuum to its
speed in a material .
Let the focal length of the convex (glass) lens be f1 and
the
focal length of the combination of this lens and the Plano
convex liquid lens be f. then:
1
1
1
=
+
𝑓 𝑓1 𝑓2
---(1)
From lens maker’s formula:
1
1
1
= (𝑛 − 1)[ − ]
𝑓2
𝑅1 𝑅2
Since f1 and f are known, the value of (f2) can be
calculated from (1).
Procedure:1:- The plane mirror is placed on the base of the stand
with the pin held
horizontally by the clamp above.
2:-The convex lens is then placed on the mirror, and its
focus is found by
locating the position of the pin where it coincides with its
own image. By
measuring from this point to the lens, its focal length (f1)
is found.
3:- The lens is now removed, and a few drops of liquid
are placed on the
mirror. On placing the convex lens on the liquid, a
combination of a
convex (glass) and a Plano-concave (liquid) lens results.
4:- The focal length (f) of the combination is found as
above, and the
focal length (f2) of the liquid lens calculated from f and f1
(eq. (1)).
5:- The radius of curvature (R) of the lens surface in
contact with the
liquid is now obtained by
a spherometer ,
6:- Calculate the
refractive index of liquid
from equation (2).
Diagram:
Observation Table:
Arrangement
Distance Of
needle tip
Focal
Length (x)
From lens
From mirror
mean
Without
liquid
(Only Convex
Lens )
19.9cm
20cm
19.95cm
f1=19.95cm
With Liquid
(Convex Lens
+Liquid Lens)
29.7cm
30.1cm
29.9cm
f=29.9cm
1.Rough Focal Length of convex lens= 10 cm
2.Radius of Curvature (determined by
spherometer)=20.03cm
Calculations
Refractive Index
1
1 1
= −
𝑓2 𝑓 𝑓1
Therefore f2=59.94cm (By substituting values from
observation table)
𝑅
𝑛 =1+
𝑓2
20.03
=1+
Therefore, n
59.94
=1.334
Precautions:
1. The liquid taken should be transparent.
2. Only few drops of liquid should be taken so that its
layer is not thick
3. The parallax should be removed tip to tip.
Sources of Error:
1.Liquid may not be quite transparent.
2.tha parallax may not be fully removed.
Bibliography:
1)http://www.physicspages.com/2014/09/16/
2)
http://physics.stackexchange.com/questions/127037/canyou-explain-fermats-principle-to-me
3) http://hyperphysics.phy-astr.gsu.edu/hbase