Liquid Prism

7/27/2019 Liquid Prism

1/16

2014

Rahul Sahu

12th A

Nirmal Higher

Secondary School

PHYSICS PROJECT


2/16

Nirmal Higher

Secondry School(Affiliated to C.B.S.E.)

Session : 2013-14

A Physics Investigatory Project to find the

Refractive index of various liquids using aLiquid Prism

Submitted to: Submitted by:

Mr. Suresh G. Kurup Rahul Sahu

H.o.d. Physics 12th

science

Roll no. = 20


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Certificate:

This is to certify that Rahul Sahu of class 12th

A has satisfactorily completed the project

in Physics on the topic Liquid Prism in the

academic year 2013-14. The project has been

completed under my supervision fulfilling the

required conditions. I have examined the

project and hereby accord my approval of it.

Mr. Mathew Mr. SureshKunnel G. Kurup

(Head of Institute) ( H.O.D Physics)


4/16

Acknowledgement:

As a student of class 12th, I did this project as a part of my

studies entitled Liquid Prism.

My project can never begin without you, dear GOD. Rather

than saying thank you to you, you know that Ifeel like

saying I love you, to you, always.

I must say thanks to my parents who provide me

sufficient money and help in making of this project.

Mr. Suresh G. Kurup, you are real foundation of the

project done by me. My project would never have been

possible without your guidance. Thank you very much.

Special thanks to my Principal who gave support to me.

Next on my thanks lists are my friends, teachers, students who

really showered constructive feedbacks and suggestions

without which this project would not have been in its present

form.

Rahul Sahu


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CONTENTS :

1. Objective

2. Introduction

3. Apparatus

4. Theory

5. Procedure

6. Observations

7. Diagrams

8. Calculations + Graphs

9. Precautions

10. Result

OBJECTIVES :To study the variation of the angle of

deviation with the angle of incidence

using Hollow Glass Prism and to

determine the angle of minimum

deviation.


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To find out the refractive index, speed oflight in various liquids using a Hollow

Prism.

INTRODUCTION :

This project is of Investigatory Type. In this project, a

hollow prism has been used to calculate the refractive

index of various liquids. The hollow prism is filledwith liquid and then the experiment is performed.

APPARATUS :

Sheet of Paper

THEORY :

Refraction :In a homogenous medium, light travels along a straight line, but

whenever it falls on a surface of another medium, a very small

fraction of it is reflected back and most of the light passes into the

medium, though with a change of direction. This phenomenon of the

bending of light at the surface of separation of the two medium is

called refraction of light.


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Cause of refraction :

This phenomenon of refraction takes place when a beam of light

enters a medium in which light enters a medium in which light travels

with a different velocity.

Laws Of Refraction :

1. The incident ray, the refracted and the normal to the surface

at the point of incidence lie on the same plane.

2. For any two given media, the ratio of the sine of the angle of

incidence to the angle of refraction is a constant, where it is

the angle of incidence and is the angle of refraction.

Medium :The surrounding substance through which the light travels.

For a monochromatic light, the ratio of the sine of the angle of

incidence to the sine of angle of refraction is a constant for any two

given media. If `I is the angle of incidence, and `r is the angle of

refraction, then:

Sine(I)/Sine(R)=constant

the constant is called the Refractive Index. For most purposes it may

be assumed that the refractive index is with respect to air.

When light travels from a rarer to a denser medium, it bends towardsthe normal and vice versa when it goes from a denser to a rarer

medium. It has been experimentally shown that

Velocity of light in air

Refractive index of substance = -----------------------------------------

Velocity of light in substance


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Refraction Through Prism:

A transparent medium bounded by two plane surface inclined to each

other at an angle is called a Prism. The angle between the two faces

is known as the angle of the prism.

Angle of deviation: The angle through which the incident ray of

light is deviated is called the angle of deviation. In fact it is the angle

between the emergent ray and the incident ray produced.

Angle of minimum deviation: As the value of the angle of incidence

(i) increases, the angle of deviation decreases till for a particular value

of the angle of incidence, it attains a minimum value Dm, is called the

angle of minimum deviation.

Critical angle : It is that angle of incidence in the denser medium for

which corresponding angle of refraction in the rarer medium is 90

degree.

= 1/sin C

Where,

- Refractive Index

C- Critical angle

The four factors on which angle of deviation depends are :

1. Angle of prism ( A )

2. Material of prism ()

3. Angle of incidence ( I )

4. Wavelength or colour of light ( )

Theory on refraction through Prism :

When a ray of light passes from one medium into the other, it eitherbends towards the normal or away from the normal in the second


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medium, depending upon whether the second medium is denser or

rarer with respect to first medium. This phenomenon is known as the

Refraction of light.

For a particular pair of two media, and for a particular wavelength of

light (colour) the ratio of the sine of the angle of incidence and the

sine of the angle of refraction is a constant quantity called the

Refractive Index of the second medium with respect to the first

medium. It is represented by:

= Sin i/Sin r

Therefore, the value of the angle of incidence i can be obtained in

terms of the refracting angle A of the prism and the angle of minimum

deviation m and the angle of refraction r can also be obtained in

terms of the refracting angle A of the prism.

Let ABC represent a section of the glass prism and let IP be a ray

incident at angle ion the first face AB of the prism at a point P.

N1PN is the normal to this face. The material of the prism is denser

with respect to air, as such the ray will refract in the direction PQ

making an angle r1 with the normal reaching the second face AC of


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the prism at the point Q making an angle r2with the normal N2QT.

The ray emerging in the direction QE bending away from the normal

and making an angle ewith the normal.

If the incident ray IP be produced backwards to meet QE produced at

S, the angle KSQ is called the angle of deviation is represented by D.

Angle BAC is called the refracting angle of the prism and represented

by A.

To derive the relation:

A + D = i + e

In SPQ,

PS is produced to K.

KSQ or D is the external angle.D = SPQ + SQP= i-r1 + e-r 2

= (i + e) - (r 1+ r 2) ...........(1)

r1 + r2+ PTQ = 1800r 1+ r2= 180

0 - PTQ .........(2)

Taking quadrilateral APTQ

APT + AQT = 900 + 900= 1800A + PTQ = 1800 A = 180 - PTQ --------(3)From (2) and (3)

r1 + r2 = A ...........(4)From (1) and (4)


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D = i + e - AA +D = i + eWhen the angle of deviation D has minimum value Dmthe followingconditions are fulfilled: i = e and r1- r2 = r (say)

Applying these conditions in Eq.(2) and (3)

A = 2 r

or r=A/2 --------(5)

and A + D m = 2i

i= ( A+Dm)/2 ---------(6)

Since, 2 = sin i/sin r

We obtain on substituting the value of (i) and (r)

Since, = Sin(i)/Sin(r)

= (Sin(A+Dm)/2)/Sin(A/2) ------------(7)

Thus we find that we can use the relation (7) for determining the

refractive index. The experiment thus consists of finding of the value

of the refracting angle of minimum deviation Dm.

For finding the value of Dma curve is plotted between the angles of

incidence (i) and their respective angles of deviation (D).

PROCEDURE :

Fix the sheet of white paper on Drawing board with cello tape ordrawing pins.

Draw a straight-line XY nearly at the centre of the sheet parallelto its length. Mark points marked as O at suitable spacing on

the line XY and draw normal to the line XY at point O. Draw


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straight line PQ corresponding to the incident rays that are

drawn at the angles of incidence ranging from 30 to 60 i.e. for

angles 35,40,45,50,55 & 60 using a protractor.

Fill the liquid from open and of prism. Fix two pins P and Q about 8 cm on the incident ray line and

view its image with one eye closed from the side of BC of the

prism. Fix two pins R and S on the paper such that the tips of

these pins and the tips of these images of the incident ray pins,

all lie on the same straight line.

Join the points (i.e. pin pricks) S & R and produce it backwardsto meet the incident ray PQ produced. Thus RS is the emergent

ray corresponding to the incident ray PQ. Draw arrow heads to

show the direction of rays.

Measure the angle of deviation D with Protractor. Repeat at steps (4 to 8) for different liquids having different

values of angle of incidence and measure the corresponding

angles of deviation D. Take at least three values (i) from 300to

400.

Now place the prism on separate sheet of paper or on the samesheet at a suitable place and trace its triangular boundary with a

sharp pencil. Measure the angle A, of the triangle so traced with

the help of protractor.

Record your observation in observation table.Plotting of graph between i & D.

Plot a graph between angle i and D for various sets of values recorded

in the observation table.


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OBSERVATIONS :

For Water :

Sl.No. ANGLE OF

INCIDENCE

ANGLE OF

DEVIATION

1. 35o 25o

2. 40o 24

o

3. 45o 23

o

4. 50o 25

o

5. 55o

26o

For Spirit :

Sl.No. ANGLE OF

INCIDENCE

ANGLE OF

DEVIATION

1. 35o 29o

2. 40

o

26

o

3. 45o 25

o

4. 50o 27

o

5. 55o 28o

For Glycerin:

Sl.No. ANGLE OFINCIDENCE

ANGLE OFDEVIATION

1. 35o 39

o

2. 40o 38o

3. 45o 35

o

4. 50o 40

o

5. 55o 41o


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For Benzene:

Sl.No. ANGLE OF

INCIDENCE

ANGLE OF

DEVIATION

1. 35

o

40

o

2. 40o 39o

3. 45o 41

o

4. 50o 42

o

5. 55o 45o

CALCULATIONS :

Formula Applied :

= (Sin (A+Dm ))/2

Sin (A/2)

1. Water: = (Sin (60+23))/2 = Sin 41.5

Sin(60/2) Sin 30

= 0.6626 = 1.33

0.5

2. Spirit: = ( Sin (60+25 ))/2 = Sin(42.5)

Sin(60/2) Sin 30

= 0.6756 = 1.35

0.5

3. Glycerin: = (Sin(60+35))/2 = Sin(47.5)


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Sin(60/2) Sin 30

= 0.7372 = 1.47

0.5

4. Benzene : = (Sin(60+39))/2 = Sin(49.5)

Sin(60/2) Sin 30

= 0.7600 = 1.52

0.5

Precautions :

A sharp pencil should be used for drawing the boundary of theprism.

The separation between the pins should not be less than 8 cm. The angle of incidence should lie between 30-45. The same and prism should be used for all observations. So an

ink mark should be placed on it to distinguish it as a refracting

angle A of the prism.

The pins should have sharp tips and fixed vertically and the pinpricks should be encircled immediately after they are removed.

Proper arrow should be drawn to indicate the incident, therefracted and the emergent rays.

A smooth curve passing practically through all the plotted pointsshould be drawn.


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RESULTS :

The angle of deviation, Dfirst decrease with the increase in theangle of incidence, attains a minimum value and then increasewith further increase in angle of incidence.

The angle of minimum deviation Dmfor :1.) Water = 23

o

2.) Spirit = 25o

3.) Glycerine = 35o

4.) Benzene = 39o

The refractive index of :1.) Water = 1.33

2.) Spirit = 1.35

3.) Glycerine = 1.47

4.) Benzene = 1.52

The speed of light in :1.) Water = 2.26 x 10

8m/s

2.) Spirit = 2.22 x 108m/s

3.) Glycerine = 2.04 x 108m/s

4.) Benzene = 1.97 x 108m/s

Liquid Prism

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