Physics Final

To study various factors on which the internal resistance of cell depends A Project Report  Submitted by

Pranjal Mehta  In partial fulfillment of of the

CBSE GRADE XII IN Physics At

AECS MAGNOLIA MAARUI PUBLIC SC!OOL Arakere, Off Bannerghatta Road, Bangalore-560076

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CERI(ICAE

This This is to cert certif ify y that that Pran Pranja jall Meht Mehtaa of rad radee !"", !"", A#$% #$% MA& MA&O' O'"A "A MAAR(T"

P(B'"$

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BA&A'OR#

*ith

Roll

&+er  er 

 ........... has satisfactorily co/leted the /roject in Physics on actors aff affect ecting ing the inter nterna nall resi resist stan ance ce of a cel cell in /art /artia iall f+lf f+lfil ill len entt of the re1+ re1+ir ire een ents ts of All "ndi "ndian an %eco %econd ndar ary y %cho %chool ol $ert $ertif ific icat atee #2a #2ain inat atio ion n 3A"%%$#4 as /rescried y $B%# in the year 0-58

Signature Signature of the Candidate Candida te

Signature of the Principal

of

the Teacher Teacher In-Charge In-Cha rge

Signature of the External Examiner 

AC)NO*LEDGEMEN " *arly ackno*ledge the contin+o+s enco+rageent and tiely s+ggestions offered y o+r dear Princi/al 9r8%eea oel8 " e2tend y hearty thanks for  gi:ing e the o//ort+nity to ake +se of the facilities a:ailale in the ca/+s to carry o+t the /roject s+ccessf+lly8

" a highly indeted to Mrs8 ayathri, Mrs8 &a;ia and Mr8
inally " e2tend y gratef+lness to one and all *ho are directly or indirectly in:ol:ed in the s+ccessf+l co/letion of this /roject *ork8

Signature of the   Candidate

CONENS

SL NO

OPIC

Pa,e no

$

Are:iations

$

"

"ntrod+ction

"

-

Theory

%

%

%co/e and 'iitations

.

'

Ojecti:e

/

.

A//arat+s

0

/

$irc+it diagra

$"

0

Proced+re

$-

1

Oser:ation

$'

$#

Res+lt and $oncl+sion

$/

$$

Biliogra/hy

$0

ABBRE+IAIONS

 Ph ysic al Qu ant it y

Sy mbol

Un it

electric charge

Q

coulomb

Un it  Ab bre via ti o n

C

electric current

I

ampere

A

voltage, potential diference electromotive orce

V

Volt

V

E or  Є 

Volt

V  

internal resistance

R

Ohm

Ω

Resistance

R

Ohm

Ω

Capacitance

C

arad



 

 

 Ba la nc in g le ng th 1

(l )

Centi meter 

Cm

 Ba la nc in g le ng th 1

(l )

Centi meter 

Cm

1

2



INRODUCION

There is a great need of atteries in o+r daily +se electronic a//liances and the +se is increasing e:ery day8 ro la/to/ to tele:ision reotes to clocks to oile /hones, alost e:ery ho+sehold a//liance r+ns on atteries in the  /resent scenario8 Batteries are the ackone of handheld and /ortale de:ices8 "t is hard to iagine a *orld *itho+t atteries8 This rings the need to ake  /o*erf+l long lasting atteries, so as to ens+re sooth, +nhindered r+nning of  these a//liances8

=ith the o:e fro analog to digital, ne* deands are /laced on the attery8 (nlike analog /ortale de:ices that dra* a steady c+rrent, the digital e1+i/ent loads the attery *ith short, hea:y c+rrent s/ikes8 %oe a//liances need high :al+es of c+rrent8 Many failed atte/ts ha:e een ade to free a fe* de:ices like /rinters of  *ires8 The si/le reason ehind this is the inaility of efficient long lasting  atteries to deli:er eno+gh c+rrent to r+n these de:ices8 This akes is lo* internal resistance a :ery i/ortant factor to allo* gro*th of  the electronic a//liance ind+stry and ake ore and ore de:ices /ortale8 Meas+red in illiohs, the internal resistance is the gatekee/er that, to a large e2tent, deterines the r+ntie8 The lo*er the resistance, the less restriction the  attery enco+nters in deli:ering the needed /o*er s/ikes8 A high = reading can trigger an early >lo* attery> indication on a seeingly good attery eca+se the a:ailale energy cannot e deli:ered in the re1+ired anner and reains in the attery8 One coon ty/e of cell is 'eclanche cell, nae after its in:entor eorges 'echlanche8 =e +se a 'eclanche cell this e2/erient8 B+t, the res+lts of this e2/erient can e e2tended to all cells in general as ost cell constr+cts ha:e the sae asic /rototy/e, the only differences are aterials 3electrodes and electrolytes4 +sed8

 Th+s , this /roject is aied at st+dying the effect of factors like? • • •

9istance et*een the electrodes Area of electrodes di//ed in electrolyte $oncentration of electrolyte

on the internal resistance of a cell y /ractical analysis in the laoratory8 The res+lts of this e2/erient can e +sed to increase the efficiency of cells y adj+sting the factors entioned ao:e in a *ay that inii;es the internal resistance of a cell8

@

!EOR2 Electroche3ical Cells

These cells *ork on o2idation and red+ction reactions to /ro:ide +sef+l electrical energy8 A si/le electrocheical cell can e ade fro co//er and ;inc etals *ith sol+tions of their s+lfates8 "n the /rocess of the reaction, electrons can e transferred fro the ;inc to the co//er thro+gh an electrically cond+cting /ath as a +sef+l electric c+rrent8 An electrocheical cell can e

created y /lacing etallic electrodes into an electrolyte *here a cheical reaction either +ses or generates an electric c+rrent8 #lectrocheical cells *hich generate an electric c+rrent are called :oltaic cells or gal:anic cells, and coon atteries consist of one or ore s+ch cells8

Leclanche Cell "t is a ty/e of electrocheical cell8 "n 'eclanche cell the de/olari;er, *hich consisted of cr+shed anganese dio2ide,is /acked into a /ot, and a caron rod is inserted to act as the cathode8 The anode, *hich is a ;inc rod, is then iersed along *ith the /ot in a sol+tion of aoni+ chloride8 The li1+id sol+tion acts as the electrolyte, /ereating thro+gh the  /oro+s /ot to ake contact *ith the cathode8

Internal Resistance The internal resistance of a cell is the resistance offered y its electrolyte to the flo* of ions 8 Batteries can e a//ro2iately odeled as a :oltage so+rce in series *ith a resistance8 The internal resistance of a attery is de/endent on the s/ecific attery>s si;e, cheical /ro/erties, age, te/erat+re and the discharge c+rrent8 "t has an electronic co/onent d+e to the resisti:ity of the  attery>s co/onent aterials and an ionic co/onent d+e to electrocheical factors s+ch as electrolyte cond+cti:ity, ion oility, and electrode s+rface area8  The internal resistance of a cell

•

is directly /ro/ortional to the distance et*een the electrodes8 is in:ersely /ro/ortional to facing s+rface area of the electrodes in

•

electrolyte8 is in:ersely /ro/ortional to concentration of electrolyte8

•

The internal resistance of a cell is gi:en y

l 1− l 2

r3

*here

l1

,

l2

l1

4R 

are the alancing lengths *itho+t resistance and *ith

resistance 3sh+nt4 , res/ecti:ely and R is the sh+nt resistance in /arallel *ith the gi:en cell8

5

SCOPE AND LIMIAIONS The ojecti:e of this e2/erient is To st+dy :ario+s factors on *hich "nternal resistanceC#M of a cell de/ends  8

 This e2/erient hel/s +s to +nderstand the efficiency of a cell and factors affecting internal resistance8 The res+lts otained fro this e2/erient *ill gi:e the ans*ers to the D+estions? *hat ste/s can *e take to red+ce internal resistanceE , ho* can a2i+ efficiency e otained thro+gh feasile *aysE ,$an f+ll efficiency e otained at allE )o*e:er there are liitations to this e2/erient on the fact that a co/lete and s+ccessf+l res+lt *ill re1+ire high technical assistance and high le:el e1+i/ent, *hich cannot e ac1+ired at the c+rrent stage8 +rtherore the ans*er to these 1+eries *ill re1+ire high le:el e2/ertise and intellect8 Any ho* *e can ans*er soe /art of these 1+eries thro+gh /ractical e2/erientation *hich *o+ld e j+st eno+gh for o+r le:el of intellect8

6

OB4ECI+E

To study various factors on which the internal resistance of cell depends

7

APPARAUS

•

•

A /otentioeter , attery  attery eliinator 

•

t*o *ay keys

•

rheostat of lo* resistance

•

a gal:anoeter

•

a high resistance

•

an aeter

•

a cell 3leclanche or daniel cell4

•

a jockey

•

a set s1+are connecting *ires

8

Potentio3eter A /otentioeter is an instr+ent for eas+ring the /otential 3:oltage4 in a circ+it8 Before the introd+ction of the o:ing coil and digital :olt eters, /otentioeters *ere +sed in eas+ring :oltage, hence the >-eter> /art of their nae8 "n this arrangeent, a fraction of a kno*n :oltage fro a resisti:e slide *ire is co/ared *ith an +nkno*n :oltage y eans of  a gal:anoeter 8 The sliding contact or *i/er of the /otentioeter is adj+sted and the gal:anoeter   riefly connected  et*een the sliding contact and the +nkno*n :oltage8 The deflection of the gal:anoeter is oser:ed and the sliding ta/ adj+sted +ntil the gal:anoeter no longer  deflects fro ;ero8 At that /oint the gal:anoeter dra*s no c+rrent fro the +nkno*n so+rce, and the agnit+de of  :oltage can e calc+lated fro the /osition of the sliding contact8 This n+ll  alance eas+ring ethod is still i/ortant in electrical etrology and standards *ork and is also +sed in other areas of electronics8

Battery Eli3inator   A attery eliinator is a de:ice /o*ered y an electrical so+rce other  than  attery, *hich then con:erts the so+rce to a s+itale 9$ :oltage that ay e +sed y a second de:ice designed to e /o*ered y atteries8 A attery eliinator eliinates the need to re/lace atteries +t ay reo:e the ad:antage of /ortaility8 A attery eliinator is also effecti:e in re/lacing osolete designs8%oe e2a/les of attery eliinators incl+de the nine :olt ains /o*er s+//ly, the si;e and sha/e of a PPF attery, originally intended

F to re/lace the attery in /ortale radios in the F60s8 A solar /anel /ro:iding /o*er for  a /ortale a//liance ay also e considered a attery eliinator8 The ter is also soeties +sed as a isnoer *hen +sing a igger attery for ore r+ntie *hen ranching o+t a /o*er s+//ly to *ired electrical e1+i/ent +sing 9$ in/+t8

Rheostat Rheostat, adj+stale resistor   +sed in eleent can e a etal *ire or rion, caron, or a cond+cting li1+id, de/ending on the a//lication8 or a:erage c+rrents, the etallic ty/e is ost coonG for :ery sall c+rrents, the caron ty/e is +sedG and for large c+rrents the electrolytic ty/e, in *hich electrodes are /laced in a cond+cting fl+id, is ost s+itale8 A s/ecial ty/e of rheostat is the /otentioeter , an instr+ent that eas+res an +nkno*n :oltage or /otential difference y alancing it, *holly or in /art, y a kno*n  /otential difference8 A ore coon /otentioeter is si/ly a resistor *ith t*o fi2ed terinals and a third terinal connected to a :ariale contact arG it is +sed for s+ch /+r/oses as a :ol+e control in a+dio e1+i/ent a//lications that re1+ire the adj+stent of c+rrent or the :arying of  resistance in an electric circ+it8 The rheostat can adj+st generator characteristics, di lights, and start or control the s/eed of otors8 "MA#%

Gal5ano3eter

A gal:anoeter is a ty/e of sensiti:e aeter ? an instr+ent for  detecting electric c+rrent8 "t is an analog electroechanical act+ator  that  /rod+ces a rotary deflection of soe ty/e of /ointer in res/onse to electric c+rrent flo*ing thro+gh its coil in a agnetic field8 al:anoeters *ere the first instr+ents +sed to detect and eas+re electric c+rrents8 %ensiti:e gal:anoeters *ere +sed to detect signals fro long s+arine cales, and to 0 disco:er the electrical acti:ity of the heart and  rain8 %oe gal:anoeters +se a solid /ointer on a scale to sho* eas+reents, other :ery sensiti:e ty/es +se a iniat+re irror and a ea of light to  /ro:ide echanical a/lification of lo* le:el signals8 "nitially a laoratory instr+ent relying on the #arth>s o*n agnetic field to /ro:ide restoring force for the /ointer, gal:anoeters *ere de:elo/ed into co/act, r+gged, sensiti:e /ortale instr+ents essential to the de:elo/ent of  electrotechnology8 A ty/e of gal:anoeter that records eas+reents /eranently is the chart recorder 8 The ter has e2/anded to incl+de +se of the sae echanis in recording, /ositioning, and ser:oechanis e1+i/ent8

A33eter An aeter is a instr+ent for eas+ring either  direct or alternating electric c+rrent, in a/eres8 An aeter can eas+re a *ide range of c+rrent :al+es eca+se at high :al+es only a sall /ortion of the c+rrent is directed thro+gh the eter echanisG a sh+nt in /arallel *ith the eter carries the ajor /ortion8 Aeters :ary in their o/erating /rinci/les and acc+racies8 The 9HArson:al -o:eent aeter eas+res direct c+rrent *ith acc+racies of fro 08 to 80  /ercent8 The electrodynaic aeter   +ses a o:ing coil rotating in the field  /rod+ced y a fi2ed coil8 "t eas+res direct and alternating c+rrent *ith acc+racies of fro 08 to 085 /ercent8 "n the theral aeter , +sed /riarily to eas+re alternating c+rrent *ith acc+racies of fro 085 *dto @ /ercent, the

eas+red c+rrent heats a therocon:erter 3theroco+/le4G the sall :oltage th+s generated is +sed to /o*er a illi:olteter8 9igital aeters, *ith no o:ing /arts, +se a circ+it s+ch as the d+al slo/e integrator to con:ert a eas+red analog+e 3contin+o+s4 c+rrent to its digital e1+i:alent8 Many digital aeters ha:e acc+racies etter than 08 /ercent8



CIRCUI DIAGRAM



PROCEDURE Step $ 8 8 @8 8

58

9ra* the circ+it diagra sho*ing the schee of connections8 $lean the ends of the connecting *ires *ith sand /a/er and ake tight connections according to the circ+it diagras8 Tight the /l+gs of the resistance o28 $heck the e88f8 of the attery and cell and see that e88f8 and see that e88f8 of the attery is ore than that of gi:en cell ,other*ise n+ll or   alance /oint *ill not e otained 3#> I#48 Take a2i+ c+rrent fro the attery , aking rheostat resistance sall8

68 To test the corrections of the connections83insert the /l+g in the key

 K 1

and note the aeter reading 8Take o+t 000 oh resistance /l+g fro resistance o28 Place the jokey first at the end P of the *ire and then at the end D8 "f the gal:anoeter sho*s deflection in o//osite direction in the t*o cases the connections are correct48 78 J8

F8

=itho+t inserting the /l+g in the key

 K 2

, adj+st the rheostat so that a

n+ll /oint is otained on the th *ire of /otentioeter8 "nsert the 000 oh /l+g ack in the /osition in resistance o2 and y slightly adj+sting the jockey near the /re:io+s otained /osition of n+ll  /oint, otain n+ll /oint /osition acc+rately, +sing a set s1+are8 Meas+re the alancing length

l1

 et*een the /oint and the end P of the

*ire8 08 Take o+t the 000 oh /l+g again fro the resistance o2 R8B8 introd+ce  /l+gs in the key

 K 1

 , as *ell as in key

 K 2

8 Take o+t sall resistance

3-5 K4 fro the resistance o2 R connected in /arallel *ith the cell8

8 %lide the jockey along the /otentioeter *ire and otain n+ll /oint8 8 "nsert 000 ohs /l+g ack in its /osition in R.B. and if necessary ake f+rther adj+stent for shar/ n+ll /oint8 @8 Meas+re the alancing length 8 Reo:e the /l+g keys at

 K 1

l2

 fro end P8

 and

 K 2

8=ait for soe tie and for the

sae :al+e of c+rrent 3as sho*n y aeter4 re/eat the ste/s 7 to @8 58 Re/eat the oser:ations for diffrent :al+es of R re/eating each oser:ation t*ice8 68 $alc+late the internal resistance of cell y +sing the ao:e relation for r8 @

Step " To see the effect of distance et*een the electrodes on internal resistances, kee/ing the other factors constant ,:ary se/aration et*een electrodes and eas+re internal resistance in each case8

Step To see the effect of area of electrodes on internal resistances, kee/ing the other factors constant , add ore electrolyte of the sae concentration and eas+re internal resistance in each case8

Step % To see the effect of concentration of electrolyte on internal resistance, kee/ing the other factors constant , decrease concentration of electrolyte y adding the distilled *ater and deterine internal resistance of cell in each case 8



OBSER+AIONS 6A78 Internal resistance o9 cell 8 'east co+nt of aeter- 080A 8 Lero $orrection in aeter- 0A @8 #M of dry cell  

%8&o8

8 8

Aeter   Reading 3A4 085 085

Pos8 of n+ll /oint 3 c 4 =ith R   =itho+t 3l 4 R 3 l 4 5 66 F 

Resistance

r3

( l −l )/ l 4R  1

R3K4

3K4

 

8J 8J

Mean internal resistance  38J N 8J4 C   806 K

6B7 o st:;y e99ect o9 separation
2

1

8 Area of electrodes  @6 c Tale for effect of se/aration et*een electrodes ?%'  &O

 

%e/aration  et*een #lectrodes d 3c4 5 

Balancing length 3c4 3 l 4

Balancing length 3c4 3 l 4

Resistanc e R3K4

F 

 FJ

 

r3

( l −l )/ l 4R  1

2

1

3K4 8J 68F

"t is oser:ed that internal resistance increases *ith increase in se/aration  et*een the8 5

6C7 o st:;y the e99ects o9 area o9 electro;es 1. EMF of cell = 2v 2. Distance between electrodes = 2.5 cm  Table for Eect of area between electrodes SL !

"rea of Electrodes #cm$2%

&alanci n' Len't(#l 1%   #cm%

1

15.*

21+

2

+1.*

2+1.5

&alancin )esistan ' ce )3K4 Len't(#l 2%   #cm% +1 2 +8

2

r3

( l −l )/ l 4R  1

2

1

3K4

1., 1.-5

 T(is s(ows t(at internal resistance is inversel /ro/ortional to area between electrodes.

6D78 o st:;y the e99ect o9 concentration o9 electro;e 18 #M of the cell  : 8 9istance et*een electrodes d 85c

@8 Te/erat+re  5$ 8 Area of electrodes A @8 c8 %'  &O

8 8

$onc of  Balancing Balancing #lectrolyte length 3l4 'ength   3c4 3l4   3c4 A @ @ B



Resistance R3K4

F

r3

( l −l )/ l 1

2

1

4R  3K4



86J



875

 "0&  T(is s(ows t(at internal resistance of a cell is inversel /ro/ortional to t(e concentration t(e electrolte 6

RESUL > CONCLUSIONS

4 The ef of a cell is constant #





4 The internal resistance of a cell is ;irectly  /ro/ortional to the se/eration  et*een the electrodes @4 The internal resistance of a cell is in5ersely /ro/ortional to the area of  the electrodes di//ed in electrolyte 4 The internal resistance of a cell is in5ersely /ro/ortional to the concentration of electrolyte

7

BIBLIOGRAP!2

=iki/edia8org Physics*orld8co ho*st+ff*orks8co khanacadey8orgCscienceC/hysics hy/er/hysics8/hy-astr8gs+8ed+C oogle "ages Practical Physics - $lass!""

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