Post on 26-Feb-2018
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ACKNOWLEDGEMENT
Id like to express my greatest gratitude to thepeople who have helped and supported me
throughout my project. I am grateful to Mrs. SusanJohn for her wonderful support for doing this
project, from the initial advice and theencouragement to this day. his project is thecom!ined e"ort of our group, so I would like to
thank my group mem!ers for helping methroughout this project.
I furthermore thank my principal Mr. #avi homas
for providing me this project, my parents, for theirundivided support and interest which inspired meand encouraged me to go my own way, without
which I wouldnt !e a!le to complete this project. $last !ut not the least, Id like to thank my friends
who motivated me and %nally to &od, who made a
things possi!le'
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INTRODUCTION
)otentiometer is a device that can !e used to do
many things like %nding the internal resistance of
a cell or to compare e.m.fs of two cells. *ere inthis project we have found out the variation of
internal resistance with many factors.
)otentiometer is a very useful device in the %eld o
physics. Its applications are of great help in many
experiments. hrough this project we could learn a
lot a!out such uses of potentiometer.
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)otentiometer is a device used to measure the
internal resistance of a cell or to compare e.m.f of
two cells and potential di"erence across a resistor
PRINCIPLE:-
It works on the principle that when a constantcurrent ows through a wire of uniform thickness
and material , potential di"erence !etween its two
points is directly proportional to the length of the
wire !etween the two points .
# - pl $
/ - 0 Ip $ 1 l
2ut Ip $ is a constant
i.e. / 3 4
5r /-kl
where k is constant of proportionality. It is called
the potential gradient along the potentiometer
wire and measured in /m6(.
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WHEATSTONES BRIDGE PRINCIPLE
8our resistors ), 9, # and S are connected so as toform a :uadrilateral ;!ridge< with a &alvanometer
in the middle. If the resistors are connected such
that the ratio of ) and 9 e:uals ratio of # and S,
then no current passes through the galvanometer
his condition is known as 2alanced =ondition ofthe >heatstones 2ridge.
$t 2alanced =ondition, )9 - #S .
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CONSTRUCTION:-
$ potentiometer consists a long wire of uniform
cross sectional area , usually ? to (@ m long , of
material having high resistivity and low
temperature coeAcient such as constantan or
manganin. hese wires are stretched parallel to
each other on a !road wooden !oard !y the side
at a metre scale. $ !attery of constant e.m.f. is
connected to the two ends. $ jockey with a
sensitive &alvanometer is made to slide on the
wire.
WORKING:-
$ fully charged 2attery eliminator having aconstant and high e.m.f. is connected !etween
terminals ) and 9 through an ammeter and
#heostat . his provides an adjusta!le potential
gradient along the potentiometer wire. )ositive
terminal of the !attery is connected to terminal ).)ositive terminals of other cell or cells are also
connected to same terminal ).
$dvantages of potentiometerB6
C
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Dasy to use
4ow cost
*igh amplitude output
Dasily availa!le
$pplications of a potentiometerB6 4inear displacement measure
#otary encoders
/olume control
Compariso o! ".m.!.s o! #$o %"&&s
>ith the help of a voltmeter we can measure onlythe terminal potential di"erence of a cell, !ut using
potentiometer we can determine the value of e.m.f.
of a given cell. he e.m.f. of the auxiliary !attery is
constant and more than that of given cell. >hen a
key is inserted, a constant current I ows through thpotentiometer wire and a potential gradient is set
up.
he positive terminals of the cells D(and D+ are
connected to the Eero end terminal of the
potentiometer, whereas the negative terminals areconnected through a two way key to a galvanometer
$ resistance !ox and a jockey.>hen the cell D( is in
circuit, on sliding the jockey gently along the
potentiometer wire a point J, say l(distance from the
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Eero end, is o!tained where the galvanometer shows
Eero deection. In such case the negative terminal o
the cell D(and the point J on the wire are at same
potential. *ence, fall of potential along the length l(
of the potentiometer wire is e:ual to the e.m.f. of thecell D(as no current is drawn from the cell. $s the fa
of the potential along a wire of uniform area of cross
section is proportional to its lengthG
D(3 l(
D( - k l( ''''''''''''..;(here k is the potential gradient along the
potentiometer wire.
Similarly, a point at a distance l+from Eero end of thwire can !e o!tained with the cell D+ , where the
galvanometer shows Eero deection, so that again
D+-k l+ ''''''''''''..;+