Sachdeva millennium school
PhysicsProject
Topic : Study of various factors on whichthe
internal resistance/EMF of a cell
depends.
Submitted to : Mr. Vishal Sir
Submitted by: Harsh Thapliyal [class: 12 science A]

Certificate
This is to certify that Master Harsh Thapliyal , a
student of class 12th
(science)A has successfully
completed his project work under the guidance of
subject teacher Mr. Vishal Sir during the year
2018/2019 from Sachdeva millenniumschool in
partial fulfillment of physics practicle examination
conducted by CBSE.
Teacher In-charge External Examiner
Principal School Rubber Stamp

Acknowledgement
The success and finaloutcomeof this project requireda lot
of guidanceand assistancefrom manypeopleand I am
extremelyfortunateto have got this all along the completion
of my project work. Whatever I have doneis onlydue to such
guidanceand assistanceand I would not forget to thank
them.
I respect and thank Mr. Vishal sir, for giving me an
opportunityto do thisproject work and providingus all
support and guidancewhich made me completethe project
on time. I would liketo express my gratitudetowards for
helpingme in conductingpracticals for project.
Last but not the least I would liketo thankall my friendswho
supported me all the way and my parentswho helped me
financiallyand encouraged methroughout in the
completion of project.

INDEX
Topics
Introduction
 Internal Resistance
Practical Analysis
 Objective
 Apparatus
 Theory
 Circuit Diagram
 Procedure
 Result & Inferences
 Precautions
 Sources of error
Flowchart Conclusion
Bibliography
1.
2.
3.
4.

INTRODUCTION
There is a great need of batteriesin our dailyuse
electronicappliancesand the use is increasingevery day.
Thus , the batteries need to be made more powerful so
that their potentialcan be increased greatly .
Thus , thisproject report is based on practical analysis
for the factorsaffectingthe internal resistanceof a
cell.
When the internalresistanceof the cell is decreased
we can increasethe potential differenceacrossit , and
hence make it more reliable.

INTERNAL RESISTANCE
Internal resistance is defined as the resistance offered by the
electrolyteof the cell to the flow of ions.
 Its S.I. unit is Ohm (Ω)
For a cell of e.m.f. (E) and internal resistance (r), connected
to an external resistance (R) such that (I) is the current
flowing through the circuit,
E = V + Ir
Internal Resistance r = E–V
I

PRACTICAL ANALYSIS
OBJECTIVE
To studythe variousfactorson which the internal
resistanceof a cell depends.
APPARATUS
A potentiometer, a battery(or batteryeliminator), two
one way keys, a rheostat,a galvanometer,a resistance
box, an ammeter,a cell (Leclanchecell), a jockey, a
setsquare, connecting wires and sand paper.
THEORY
The internalresistanceof a cell is the resistanceoffered
by its electrolyteto the flowof ions. The internal
resistanceof a cell
 Is directlyproportionalto the distancebetween
the electrodes.

r = (E-V)/I
 Is inverselyproportionalto facingsurfacearea of
the electrodesin electrolyte.
 Decreaseswith increasein temperatureof electrolyte.
 Is inverselyproportionalto concentration
of electrolyte.
The internalresistanceof a cell is given by:
CIRCUIT DIAGRAM

PROCEDURE
1.Clean the ends of the connecting wires with sand
paper and make tight connectionsaccordingto
the circuit diagram.
2. Tighten theplugs of the resistance box.
3. Check the e.m.f. of the batteryand of the cell and
make sure that e.m.f. of the batteryis more than that
of the cell, otherwisenull or balancepointwill not
be obtained.
To studyvariation of internal resistance with distance of
separation
4.Keep both the electrodesat a distanceof 16 cm.
5.Take maximumcurrentfrom the battery, making
rheostatresistance small.
6.Withoutinsertinga plug in key K2, adjust the
rheostatso that a null point is obtainedon the last
wire of the potentiometer.
7. Determinethe position of the null point accurately
using a set squareand measurethe balancing length
(l1) between the null point and the end P.
8.Next introduceplugsin both keys K1 and K2. At the
same time, take out a smallresistance(1 – 5 W) from

The shunt resistancebox connectedin parallel
with the cell.
9.Slidethe jockey along a potentiometer wire and
obtainthe null point.
10. Measurethe balancinglength(l2) from end P.
Record these observations.
11. Now keep the electrodes12 cm apart.
12. Then removethe plugs of keys K1 and K2. Wait
for sometimeand repeat steps 7 to 10.
13. Next, keep the electrodes 9 cm apart to obtain
anotherset of observations.
To studyvariation of internal resistance with area of
electrodes
14. Keeping all other factorsconstant, increase
the area of electrodes in the electrolyteby dipping
them intothe electrolyteat differentdepthsfor each
observation.
15. Obtain three such observations by
repeating steps 7 to 10. Record your readings.
To studyvariation of internal resistance with
concentration of electrolyte

16. Keeping all other factors constant,decreasethe
concentrationof electrolyteby addingdistilledwater
for differentobservations.
17. Obtainthreesuch observationsby repeating step
7 to 10. Record your readings.
OBSERVATIONS
S.no. Ammeter
Reading
(A)
Position of null point(cm) Shunt
Resistance
R(Ω)
Internal
Resistance
r(Ω)With R
(l1)
Without R
(l2)
1. 0.3 660.5 35.5 1 0.94
2. 0.3 660.5 77.2 2 1.77
3. 0.3 660.5 108.3 3 2.51
Table for effect of separation between electrodes
S.no. Separation
between
electrodes
d (cm)
Balancing
point
Balancing
point
Internal
Resistance
r(Ω)
r/d
l1(cm) l2(cm)
1. 1.2 326.6 276.9 0.456 0.38
2. 2.5 320.7 219.1 0.95 0.38
3. 3.7 660.5 350.9 1.406 0.38

Table for effect of temperature
S.no. Temperature
T (o
C)
l1(cm) l2(cm) Resistance
R(Ω)
Internal
Resistance
r(Ω)
Tr
(ΩK)
1. 1.2 326.6 276.9 0.456 0.38 301.44
2. 2.5 320.7 219.1 0.95 0.38 291.96
3. 3.7 660.5 350.9 1.406 0.38 283.87
RESULT & INFERENCES
 The ElectromotiveForce of the cell is constantand
is equal to E = 0.98 Volt.
 The internalresistanceof a cell is directly
proportionalto the separationbetween the
electrodes.
 The internalresistanceof a cell is inversely
proportionalto the area of the electrodes dippedin
electrolyte.
 The internalresistanceof a cell is inversely
proportionalto the temperatureof electrolytes.
 The internalresistanceof a cell is inversely
proportionalto the concentrationof the electrolyte.

PRECAUTIONS
1.The connectionsshouldbe neat, clean and tight.
2.The plugs shouldbe introducedin the keys only
when the observations are to be taken.
3.The positive pollsof the batteryE and cells E1 and
E2 should , all be connected to the terminalat the
zero of the wires.
4.The jockey key should not be rubbed alongthe wire.
It shouldtouch the wire gently.
5.The ammeterreading should remain constant for a
particularset of observation. If necessary, adjust
the rheostat for this purpose.
SOURCES OF ERROR
1.The auxiliarybatterymay not be fully charged.
2.The potentiometer wire may not be of uniformcross-
section and materialdensitythroughout its length.
3.End resistancesmay not be zero.

FLOWCHART
CONCLUSION
Factors Affecting Internal Resistance of a Cell
Area of
Electrodes
Inversely
Proportional
Conc. of
Electrolyte
Inversely
Proportional
Distance
between
Electrodes
Directly
Proportional
Temperature
of
Electrolytes
Inversely
Proportional

BIBLIOGRAPHY
 www.google.com
 www.documents.mx
 www.wikipedia.org
 www.docfoc.com
 www.slideshare.net