phy potentiometer

7/25/2019 Phy Potentiometer

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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

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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+ ''''''''''''..;+

phy potentiometer

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