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Gyan ganga interna international tional Academy, bhopal
2015-2016
To fnd reractive indices o water and turpentine oil Submitted by :
submitted to:
Ashwin Singh prasad
r!"agendr r!"agendra a
#lass: $%% &'( )oll no!
CERTIFICATE *his to certi+y that the proect report entitled to .nd re+racti/e indices o+ water and turpentine oil submitted by Ashwin Singh during the academic year 2015 2016 is a bona.ed piece o+ wor conducted under my super/ision and guidance! *he data sources ha/e been +ully acnowledged! % wish his success in all his +uture endea/ours!
)!+ai3al sharee+ 4pgt physics
r! d!asho 4)%"#%A7
Acknowledgement
% than my physics laboratory teacher guiding me in doing this proect! 8is constant support and encouragement helped me a lot in completing this proect! % also than my chemistry teacher r! 9ai3al Sharee+ +or helping me with this proect! % also than the lab assistant and all other non-teaching sta members +or arranging the apparatus as and when re;uired! % also than my school +or pro/iding such wonder+ul laboratory +acilities!
%nde< SR. NO. 1
CONTENTS OBJECTIVE
PAGE NO. 1
2
APPARATUS
2
3
THEORY
2
4
PROCEDURE
3
5
OBSERVATION
6
CALCULATION
7
7
RESULT
8
8
PRECAUTION
8
9
SOURCES OF ERROR
9
10
BIBLIOGRAPHY
10
6
=becti/e
TOFI ND REFRACTI VEI NDI CESOFWATERAND TURPENTI NEOI LUSI NG AP ALNEMI RROR,AN EQUI CONVEXLENS( MADEOFGLASSOF KNOWNREFRACTI VEI NDEX)AND AN ADJUSTABLEOBJECTNEEDLE
Apparatus: A convex lens, an optical needle, a plane mirror, a clamp stand, a spherometer, a plumb line, metre scale, water and turpentine oil.
Theory: Let’s add small amount of water on a flat, plane surface and place a convex lens over it. This forms a plano-concave lens of water between the lower surface of convex lens and plane mirror. Let f 1 and f 2 are the focal lengths of water lens and convex lens respectivel, then focal length of the combination is! 1
F
=
1
+
1
f 1 f 2 1
The focal length of the plano-concave lens is,
1
%rom Lens &a'er’s formula,
f 1
(# ∴
)1 ( ) and )2 (
∞
(
= μ−1
)
(
μ−1 ¿
for water lens.
1
−
1
R1 R 2
1
R
)
=
1
f 1 F
−
1
f 2
"#i$
∴
The refractive index of water is ,
μ=1 +
R f 1
"#ii$
#where *)’ is the radius of curvature of the concave surfaces of the plano-concave lens$. The )adius of curvature of the lens, is
R=
l
2
6h
+
h 2
"#iii$
Procedure: I.
For finding the focal length of convex lens: #i$
&easure the rough focal length of the convex lens.
#ii$ +lace the plane mirror with the convex lens placed on it above the horiontal base of a clamp stand horiontall as its tip lies verticall above the optical centre of the lens. Adust the needle at a height a little more than the rough focal length of the convex lens. #iii$ Tr to remove the parallax between the tip of the obect needle and its image tip. #iv$ ote the distance of the tip of the needle from the centre of the upper surface of the lens. Let it be x 1. #/se plumb line$. #v$ )emove the convex lens and measure the distance of the tip of the needle from the plane mirror. Let it be x 2. #/se plumb line$.
#vi$
)epeat and record all the observations.
II. For finding the focal length of the planoconcave lens: +our few drops of water over the plane mirror and place the convex lens over it. )epeat steps #ii$ to #iv$ as done above. )epeat the procedure with turpentine oil also.
III. For finding ‘l’: 0etermine the pitch and least count of scale of the spherometer. +lace the spherometer on the dried surface of the convex lens. Turn the screw downwards ver gentl till the tip of the screw ust touches the lens. )ead and record the reading.
eep the spherometer’s legs on the base of a paper and adusting the central screw, find the pric's A, and 3 of the three legs of the spherometer. 4oin the centres of the three pric's and measure the lengths with the half-metre scale. ote the values of A, 3 and A3.
9ig: (a) to fnd ocal length o convex lens (b) or the length o legs AB, B, A o the
sphero!eter
9ig: to .nd +ocal length o+ the plano conca/e lens
"bservations +itch of the spherometer( 1 cm Least count of the spherometer ( 5.51 cm 0istance between the legs! #1$ #2$ #6$
A 3 3A
( 6 cm ( 6 cm ( 6 cm
Table for calculation of ‘h’ 7. o
8nitial reading of the 3.7. on the convex lens
o. of complet e rotation s
%inal reading of the c.s on the glass
Addition h(n &ean al 3.7 x :h; div. pitch moved 9 m x L.3
#a$
#n$
slab
1
<2
5
<.=
==.=
2
5
?
<5
5.== = 5.<
5.=>> =
To measure focal length f‘ of convex lens
.ithout li/uid
*
#istance o needle tip ro! Tip o the pper upper surace surace o the convex o the lens plane ' !irror ' * 01%2 0 05%3 03%*
.ith water .ith oil
* *
0%7 03%2 6%7 1%7
Area between lens and plane !irror
$%& o
0%4 04% 6%5 1,5
+ean x x 1 + x 2
-ocal lengt h
2
01%32 05%62 0%5 03%4 6%2 1%2
00%4 2 *0 7%3 0 1
A88AT9"&$ +ean distance between two legs l=
AB + BC + CA 3
0 c!
+ean h 1%3223 c! To fnd the radius o curvature o the convex lens: R=
l
2
6h
+
h 2
=2.27366 cm
+easure!ent o reractive indices o water and turpentine oil ).ith water between the convex lens and the plane !irror:
μ1=1 +
2.27366 R =1 + =1.06552 f 2 34.7
*) .ith turpentine oil between the convex lens and the plane
!irror μ2=1 +
2.27366 R =1 + = 1.22736 10 f 3
esult The reractive index o water is ; %1522* The reractive index o turpentine oil is ; * %**305
Precautions (i)
The screw o the sphero!eter should be !oved in one direction only to avoid bac
(ii) The screw should be !oved =ust to touch the surace o the convex lens or the glass slab% (iii) The parallax should be re!oved properly% (iv) The lens and the plane !irror should be properly cleaned% (v) The convex lens o large ocal length should be used% (vi) The sphero!eter reading should be ta
$ources o error:
(i)
The distances x and x * !ay not be !easured correctly%
(ii) The value o h and l !ay not be correct% (iii) Parallax !ay not be re!oved properly% (iv) Bac
>%>7%=G)A8? 1! @>S%*S : • • •