Physics investigatory project

ESHANT SETHI XII B PHYSICS INVESTIGATORY 

PROJECT

CERTIFICATE

This is to certify that the Physics project work on “To compare/determine the E.M.Fs of the given cells using potentiometer.” is potentiometer.”  is a onafide record of work done y Master ..................... under my guidance and supervision.

TEACHER'S NAME:

THEORY:

 A. Pot ent i omet eri sadevi ceusedt omeasur e t hei nt ernalr esi st anceofcel l ,t ocompar e t hee. m. f .oft wocel l sandpot ent i al di ffer enceacr ossar esi st or .

B. Principle 

!t works on the principle that when a constant current flows through a wire of uniform thickness and material" potential difference etween its two points is directly proportional to the length of the wire etween the two points. !t is a device used to measure the internal resistance of a cell" to compare the e.m.f of two primary cells etc. # $%&

V = IR

 R =l

V =

)et

l

 I l  A

k = I 

# $'&

 A

l  A

# $(&

l

 * constant

i.e."

v =kl

+here k  is constant of proportionality. proportiona lity. !t is called ,potential ra!ient" along the potentiometer wire and measured in -m %. C. Constr#ction

 potentiometer consists a long wire of uniform thickness crosssectional area" usually 0 to %1m long" of material having high resistivity and low temperature coefficient such as constantan or manganin. These wires are stretched parallel to each other on a oard wooden oard y the side at a metre scale. The wires are joined in series y thick copper strips.  attery of constant e.m.f is connected to the ends P and 2 of wire" called driving or au3iliary cell" a jockey 4" with a sensitive galvanometer galvanometer 5" is made to slide on the wire P2.

6imilarly" a point at a distance  from the 7ero end of the wire P2 can e otained with the cell " where the galvanometer shows 7ero deflection" so that again l2

E2

# $'&

 E 2= k l 2

8ividing e9uation $%& y $'&"  E 1  E 2  E 1  E 2

=

=

kl 1 kl 2 l1 l2

=

l1 l2

Materials Re$#ire!:

Potentiometer" a galvanometer" a attery eliminator" a rheostat of low resistance" a resistance o3" a one way key" a two way key"  jockey" a set s9uare" connecting connecting wires and a piece of sand paper.

OBSER%ATION: %. E.M.F of attery eliminator  E.M.F of cells lkaline utton cell
*0v

* %.:;v * %.=>v

 $nippo&  $Eveready&

* %.:?v * %.:1v

8ry cell $nippo&  $Eveready&

* %.?1v * %.=:v

'. @eadings a&Aomparison etween utton cell cell and alkaline cellB
E1

&

E2 ¿

* %.:;v * %.=>v

RES'(TS: %&

'&

(&


PRECA'TIONS: %.

The connect connections ions should should e neat/ clean" and ti0t. '. The pl#s should e introduced in the keys only when the oservations are to e taken. (. The positive poles of the attery E and cells  and  should" all e connected to the terminal at the 7ero of the wires. 0. The jockey key should not e rued along the wire. !t should touch the wire gently. >. The ammeter reading should remain constant for a particular set of oservation. !f necessary" adjust the rheostat for this purpose. ;. The E.M.F of the attery should e greater than the E.M.FDs of the two cells. =. 6ome high resistance plug should e taken  E1

 E 2

out from resistance o3 efore the jockey is moved along the wire.

SO'RCES OF ERROR: %. '. (. 0.

The in instrument may e e lo loose. T0ic1 connecting wires may not e availale. @heo @h eost stat at may may hav have e hig high h res resis ista tannce. ce. The Th e au3 au3il ilia iary ry att atter eryy may may not not e 2#ll3 c0are!. >. The pot poten enttiom iometer eter wire ire ma may not e of #ni2or4 crosssection and material density throughout its length. ;. En! resistance may not e 7ero.