meghali singh

8/10/2019 Meghali Singh

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OBJECTIVE:

To determine the minimum angle of deviation

and the indices of refraction for various liquids

using a hollow prism by plotting a graph

between angle of incidence and the angle of

deviation.

The liquids used are:-

Coconut oil

Cold drink

Refined oil

Ccl4


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APPARATUSUSED

Drawing board

A white sheet of paper

HollowPrism

Drawing pins

Pencil

Half meter scale

Office pins

Graph paper

Protractor


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Theory

Refraction of light.

When light travels in a homogenous medium, it travels along a straight

path. However when it passes obliquely from one transparent medium to

another, the direction of its path changes at the interface of the two

media. This is called refraction of Light changesspeed as it moves from

one medium to another (for example, from air into the glass of theprism)

Refractive index
http://en.wikipedia.org/wiki/Speedhttp://en.wikipedia.org/wiki/Speed


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The refractive index of a medium for a light of given wavelength may be

defined as the ratio of the speed of light in vacuum to its speed in that

medium.

The refractive index of the material of the prism is given by- Draw a raydiagram for the given formula to show what A and D are.

Where Dm is the angle of deviation and A is the angle of the prism.

Factors affecting refractive index:-

Nature of that medium

Wavelength of the light used

Temperature

Nature of surrounding medium

The path along which the light travels in the first medium is called

incident ray and that in the second medium is called refracted ray.

The angles which the incident ray and refracted ray make with the

normal at the surface of separation are called angle of incidence

and angle of separation respectively

LAWS OF REFRACTION OF LIGHT

The phenomenon of refraction of light follows the following

laws:-


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First law:-the incident ray, the reflected ray and the normal to

the interface at the point of incidence, all lie in the same

plane.

Second law:-the ratio of the sine of the angle of refraction isconstant for a given pair of media.

It is observed that when a ray of light passes from an optically rarer

medium to a denser medium it bends towards normal

When a ray of light passes from an optically denser to a rare medium, it

bends down away from the normal.

A ray of light travelling along the normal passes undeflected.

Optical density is a quantity is the ratio of the speed of light in two

media while mass density is the mass per unit volume. An optically

denser medium may have mass density less than an optically rarer

medium. For example, the mass density of turpentine is less than that ofwater but turpentine is optically denser.

Physical significance of refractive index;

The refractive index of a medium gives the following two information:

The direction of bending of refracted ray. It tells whether the ray will

bend towards or away from the normal. Their refractive index is related

to the speed of light. For example ,refractive index of glass is 3/2 .thisindicates that the speed of light in glass is two third of its speed in

vacuum.


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The minimum deviation Din a prism occurs when the entering angle and the exiting

angle are the same, a particularly symmetrical configuration. Applying Snell's Law at

the interfaces you can derive the following relationship:

n=sin[(D+a)/2]/sin(a/2)

where nis the relative index of refraction of the prism, and ais the angle between the

two relevant prism faces (60 degrees in our example). Using this relationship, we

could figure out what index of refraction was assumed for this simulation. we could

also use this method to measure the index of refraction of real materials.

PROCEDURE

1. Fixed a white sheet of paper on the drawing board with the help of drawingpins or tape.

2.

Drew a straight line XX` parallel to the length of the paper nearly in the

middle of the paper.

3. Marked points q1, q2, q3.on the straight line XX` at suitable distances ofabout 5 cm.

4.

Drew normals n1q1, n2q2, n3q,..on points q1, q2,q3.

5. Drew straight lines r1q1, r2q2, r3q3, making angles of 35 , 40.60degrees respectively with the normals.


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6.

Marked one corner of the prism as A and take it as the edge of the prism for

all the observations.

7. Prism was put with its refracting surface AB in the line XX` and the pointq1in the middle of AB

8. Marked the boundary of the prism.

9.

Fixed two or more office pin P1 and P2 vertically on the line R1Q1, the

distance between the pins should be 10mm or more.

10.Looked at the images of point P1and P2 through face AC

11.Closed our left eye and brought open right eye in the line with the two

images.

12.

Fixed two office pins P3 and P 4 vertically, and 10cm apart such that the

open right eye saw pinsP4 and P3 and images P2 and P1in one straight line.

13.Removed pins P3 and P4 and encircled their pricks on the paper.

14.Repeated the steps 7 to 13with points q2,q3 .for i= 40,,60 degrees.

To measure D in different cases

15 .Draw straight lines trough points p4 and p3to obtain emergent rays

s1t1,s2t2,.

16.Produced t1s1,t2s2,t3s3,inward in the boundary of the prism tomeet produced incident rays r1q1,r2q2,at points f1,f2,f3.

17.Measured angles k1f1s1,k2f2s2,these give angle of deviation

d1,d2,d3.

18.Wrote values of these angles on paper.

To measure A


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1. Measured angle BAC in the boundary of the prism. This gives the

angle A .

2. Recorded values of observations as given below.

OBSERVATIONS

Serial no. of

observations

Angle of incidence Angle of deviation

1 35

2 40

3 45

4 50


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5. 55

*will include 6 more tables for other liquids.

CALCULATIONS

*includes graph for all the liquids.


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RESULT

i. i-D graph indicates that as the angle of incidence increases,

the angle of deviation first decreases, attains a maximum

value and then starts increasing for further increase in angle

of incidence.

ii. Angle of incidence deviation=.

iii. Refractive index of material of prism, n


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PRECAUTIONS

1.The angle of incidence should lie between 35-60 degrees.

2.The pins should be fixed vertical

3.

The distance between the two pins should not be less than 10mm.

4.Arrow heads should be marked to represent the incident and

emergent rays.

5.The same angle of prism should be used for all observations


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SOURCES OF ERROR

1..Pin pricks may be thick.

2.Measurements of angles may be wrong.


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BIBLIOGRAPHY

Immense knowledge and help was provided by the following sources:-

1.S.L.Arora guide book

2.Internet


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