MAYANK'S PRESENTATION INTERNAL RESISTENCE OF PRIMARY CELL 1.doc

8/10/2019 MAYANK'S PRESENTATION INTERNAL RESISTENCE OF PRIMARY CELL 1.doc

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ACKNOWLEDGEMENT

I Shobhit Bansal Standard XII of science

section, St. Marys Inter College, Etawah is genuinely

thankful to my teachersMrs. Sarita Anil & Mr. Edwin T.J.

for their help and guidance which I received for the

completion of my ro!ect

INTERNAL RESISTANCE OF A PRIMARY CELL

I am also thankful to our rincipal, my colleagues "

parents who have always given me their support directly or

indirectly, which was of immense help towards the

completion of this pro!ect.


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DECLARATION

I here#y declare that the pro!ect entitled

INTERNAL RESISTANCE OF A PRIMARY CELL$ is an originalwork done #y me during the year %&&'(%&&) under the

guidance " supervision of Mrs. Sarita Anil & Mr. Edwin

T.J..

Signature of *uide+ Shobhit Bansal


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CERTIFICATE

his is to certify that the investigatory pro!ect

entitled -Internal Resistance of a Primary Cell$ is an riginalwork done #y Shobhit Bansalduring %&&'(%&&) under our

supervision " guidance.

lace+ St. Marys Inter College

Mrs. Sarita Anil

Mr. Edwin T.J.

/ate+

College Seal


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INDEX

itle age 0o.

1. Introduction a2Electrochemical cells

%. rimary Cell

a2Simple 3oltaic Cell

#2/aniel Cell

c24eclaanche Cell

d2/ry Cell

5. Secondary Cells a24ead accumulator

#2Edison 6lkali Cell

7. 8utton Cell

'. 6dvantages of Secondary

Cell over a rimary Cell

). /isadvantages of Secondary Cell

9. Internal :esistance of Cell

;. Emf of a Cell


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INTRODUCTION

In present scenario human life depends upon the newinvented technologies that will #ring ease to our life. ne such

important discovery was made in 1;th century and that was the

discovery of the -power of chemicals$ i.e. electrochemical cells.

ELECTROCHEMICAL CELLS

6 cell is a chemical electrical transducer, i.e. a device

which converts chemical energy into electric energy. 6

simple cell is composed of positive and negative electrode.

>hen cell is connected across the load of electric device,the potential drop takes place and device functions. his cell has

provided us a mo#ile source of electricity. Cells are of two types +

12 rimary cell via 4eclaanche cell, /aniel cell, Simple 3oltaic

cell and dry cell etc. and

%2 Secondary cell like 4ead acid accumulator, Edison cell, etc.


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PRIMARY CELL

It is an electrochemical cell which once used cant #e put

to use again #y passing electric current.

rimary cell was accidentally discovered #y an Italian

professor -Luigi Galvani$. ?e o#served that when the nerves of a

freshly dissected frog was connected through copper and iron wire

the leg !erked violently. ?e concluded that it was due to animal

electricity in frogs leg.

4ater -Alessandro Volta$ modified his discovery anddeveloped Simple voltaic cell.

SIMPLE OLTAIC CELL

Constr!ction(

In simple voltaic cell dilute sulphuric acid work as

electrolyte. 6nd copper and @inc rod act as electrode of whichcopper rod is positive pole and @inc rod is negative pole.

ActionA

he dilute sulphuric acid dissociates as represented #elow+

?%S7 %?B B S7

%(

inc rod forms n%B as

n n%B B %e(

6s reaction proceeds concentration of n%B ion increases.

?B ions drift to the copper rod. n reaching the rod it takes an

electron " thus copper rod starts to acDuire the Bve charge due to

this potential difference set up #etween copper and @inc rod, the

ma=imum emf developed in voltaic cell is 1.&; 3.

"ANIEL CELL


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It was developed #y -Danielin the year 1orking+

In the porous pot, @inc sulphate is formed. he reactions are A

n n%B B %e(

?%S7 %?B B S7

%(

n%B B S7%( nS7

n B ?%S7 nS7 B %?B B %e(

he formation of nS7on the porous pot does not affect

the working of cell. n diffusing out porous pot ? ions react with

copper sulphate solution.

%?B B CuS7 ?%S7 B Cu%B

6s the Cu%B ions deposit on the copper vessel it acDuire

positive charge. /ue to the development of this potentialdifference, it starts to give an emf of 1.1 3.

LECLAANCHE CELL


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4eclaanche cell was invented #y -George De Leclaanche

in the year 1


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It is a porta#le form of 4eclaanche cell.

Constr!ction$

In a dry cell a moist paste of ammonium chloride

containing @inc chloride is used as an electrolyte. inc chloride

#eing highly hydroscopic, it is added to ammonium chloride in

order to keep it moistened. he paste of 0?7Cl and nCl% is

contained in a small cylindrical @inc vessel, which acts as the

negative pole of the cell. 6 car#on rod fitted with a #rass cap isplaced in the middle of the @inc vessel. It acts as the positive pole

of the cell. he car#on rod is surrounded #y a closely packed

mi=ture of Mn% and charcoal powder in a muslin #ag while the

Mn% acts as depolariser, the charcoal powder reduces the internal

resistance of the cell #y making Mn% conducting. he @inc

container and its contents are sealed at the top with pitch or shell.

Action$

6 dry cell is only a modification of wet 4eclaanche cell.

herefore, the action of a dry cell as regards the chemical reactions

takes place are same as in the case of 4eclaanche cell.

he dry cells are manufactured in different si@es and shapes to suit

particular needs. Irrespective of the si@e of the cell, the emf of the

cell is nearly 1.' 3. Its internal resistance may vary from &.1 to

1& . Gurther an electric current of a#out &.%'6 can #e

continuously drawn from a dry cell.


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SECON"ARY CELLS

6 secondary cell is one in which chemical energy is

converted into electrical energy #ut they do so only when they are

charged #y passing current through them #y some source.

hey are also called accumulators orstorage cells. hey are of two

types(

1.4ead acid cell or lead accumulator%.Edison alkali cell

LEA" ACC(M(LATOR

It is the most common type of storage #attery used in

automo#iles. It was invented #y Grench physicist, Gaston lantein

the year 1;'


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"isc)ar'in'$

>hen the cell is connected to an e=ternal load circuit, it suchcurrent in the circuit and starts discharging . he dilute sulphuric

acid dissociates into ?B and S7%( ions.

?%S7 %?B B S7

%(

6t the negative plate+

# B S7%( B %e( #S7

6t the positive plate+

#% B %?B B %e( #B?%

# B?%S7 #S7B?%

#%B?%S7B%?B B %e( #S7 B %?%

C)ar'in'(In order to charge a lead accumulator, it is connected to a

#attery charger capa#le of supplying emf greater than that of thelead accumulator. >hile charging an accumulator,a high series

resistance is included in the circuit. he #attery charger make ?B

ions to move towards negative plate and S ions towards the

positive plate.

6t the negative plate+

#S7 B %?B B%e( # B ?%S7

6t the positve plate+

#S7 B S7%( ( %e( #% B %S5%S5 B %?% %?%S7#S7B %?% B S7

%(( %e( #%B%?%S7herefore, during the charging process, #S7 at#oth

lectrodes is connected #ack into spongy lead F#2 at negative plate

and #% at positive plate.


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E"ISON AL*ALI CELL

It is also called nic!el"ironF#i"$e2 cell.

Constr!ction(

Its positive plate consists of a num#er of tu#es ofperforated steel ri##on #ound specially " held together #y steel

rings. he tu#es are nickel plated. he active material consists of

0iF?27 " flakes of metallic nickel are packed into the nickelplated steel tu#es in alternative layers.

he negative plate is made from finely perforated nickelled

steel strips, stamped into pockets. he pockets are filled with

powdered iron o=ide.

%OR*IN+(

he chemical changes during charging and dischargingcan #e represented #y the following reversi#le reaction+

0iF?27 B H? BGe 0iF?2% B H? B GeF?2%

he emf of the fully charged cell is 1.7'3 " it falls to1.%3 on discharge.


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A-.anta'es of secon-ary cell o.er a /rimary cell #

1. Secondary cell can #e put to use again and again #y

recharging it. >hile a primary cell once discharged cannot

#e recharged.

%. he internal resistance of a secondary cell is less than that

of a primary cell. 6s such a secondary cell ena#les to draw

much larger current.

"isa-.anta'es of secon-ary cell #

1. 6 secondary cell has to #e charged first so as to o#tain

electric energy from it. In other words, secondary cell

reDuires a lot of time #efore it can #e put to use, while

primary cell stsrts functioning immediately after its

construction.

%. he initial cost of a secondary cell is Duite large as

compared to that of a primary cell.


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INTERNAL RESISTANCE OF CELL

Internal resistance of a cell is defined as the

resistance offered #y the electrolyte and electrodes of a cell

when the electric current flows through it.

he value of internal resistance of a freshly prepared

cell is generally low and its value goes on increasing as the cell

is pur to more and more use.

his internal resistance has a negative effect on the

working of a cell, it reduces the efficiency of a cell.

he internal resistance of a cell depends on the following

factors+

1. /istance #etween the electrodes

%. he nature of the electrolytes

5. he nature of electrodes

7. 6rea of the electrodes immersed in the electrolyte. If area

increases, internal resistance decreases.


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EMF of a Cell

Emf of a cell is defined as the potential difference

#etween the two electrodes of a cell in a closed circuit. It is

denoted #y 3.

>hen the electric cell is in the open circuit the

current flows through the circuit. here is a fall of potenteial due to

the internal resistance of the cell. he terminal potential difference

#etween the two electrodes of a cell is less than the emf of the cell

#y an amount eDual to potential drop due to the internal resistanceof the cell. hus, the terminal potential difference of cell is always

less than the emf of the cell.

3 E ( Ir

Consider a cell of emf E and internal resistance r

which is connected to e=ternal resistance :. 6 high voltage

voltmeter is connected across the electrode of cell. >hen key H is

closed, current flows and

otal resistance : B r

Magnitude of current, I EJ:Br

otential difference across internal resistance,Fr2 Ir

Grom hms law,

3 I:

3 FEJ:Br2:

r, r FE(3J32:

6ccoding to the definition of internal resistance,

3 E ( Ir


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If I &, 3 E

he terminal potential difference across terminal of cell eDuals to

potential difference across e=ternal resistance.EXPERIMENT

O,0ECT$ To determine the internal resistance of a primary

cell using a potentiometer.

APPARAT(S $ 6 potentiometer, a #attery, two one(way keys, a

rheostat of low resistance, a galvanometer, a resistance #o=, a

!ockey, connecting wires and piece of sand paper.

THEORY $ he internal resistance of a primary cell is given #y A

r Fl1A l%2Jl% K :

?ere l1and l%are the #alancing lengths without shunt

and with shunt respectively and : is the shunt resistance.

PROCE"(RE$

1. /raw the circuit diagram.

%. Clean the ends of the connecting wires with the sand paper

and make tight connections.

5. ight the plugs of resistance #o=.

7. Check the emf of the #attery and cell, and see that emf

of the #attery is greater than the emf of the cell.'. ake minimum current from the #attery making rheostat

resistance @ero.o test the correctness of the

connections +F insert the plug in the key H and note the

reading. ake out %&&& resistance plug from the

resistance #o=2.


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). o test the correctness of the connections F insert the plug

in the key H1" note the reading. ake out the %&&&

resistance plug from the resistance #o=29. >ithout inserting the plug in the key H%ad!ust the rheostat

so that a null point is o#tained on the fourth wire of the

potentiometer.

;. Introduce the %&&& plug #ack in its position in the

resistance #o= and #y slight ad!usting the key.


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of the either of the two cells.

'. Current should #e passed for short time only, while

finding the null point.

). Cell should not #e distur#ed during e=periment.

SO(RCES OF ERROR #

1. he au=iliary #attery may not #e fully charged.

%. he potentiometer wire may not #e of uniform cross(

section and material density throughout its length.5. End resistances may not #e @ero.


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BIBLIOGRAPHY

Modern(s a)c o' hsics Satish H. *upta

*om%rehensive ractical hsics L.0. Laiswal

*once%ts o' hsics +Vol.,- ?. C. 3erma

A Tet)oo! o' Electricit /. C. andey

and Magnetism

/. E. /rodov /. 8. Singh

radee%(s $undamental hsics H. 4. *om#er

H. 4. *ogia


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MAYANK'S PRESENTATION INTERNAL RESISTENCE OF PRIMARY CELL 1.doc