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1. SATHYA VIDYALAYA SENIOR SECONDARY SCHOOL
(Affliated to Central Board of Secondary Education, Delhi)
Affliation No. 1930393
Pillaiyarkulam - 626110
An Investigatory Project Report
On
Wheatstone bridge
For
AISSCE 2024 Examination
[As a part of the Physics Course (083)]
SUBMITTED BY
G.Priyadharsan
Under the Guidance of
Mrs. Amutha Rani M.Sc., B.Ed
PGT (Physics)

2. CERTIFICATE
This is to certify that Master G.Priyadharsan, a student of class
12th
(Science Stream) has successfully completed his project work on
Wheatstone bridge under the guidance of subject teacher Mrs. S. Amutha
Rani during the year 2023 – 2024 from Sathya Vidyalaya CBSE in partial
fulfilment of physics particle examination conducted by CBSE.
I certify that this project is up to my expectations as per CBSE
guidelines.
Teacher
Mrs. S. Amutha Rani
Sathya Vidyalaya CBSE
PRINCIPAL
K. SENTHIL KUMAR

3. ACKNOWLEDGEMENT
The success and final outcome of this project required a lot
of guidance and assistance from many people and I am extremely
fortunate to have got this all along the completion of my project
work. Whatever I have done is only due to such guidance and
assistance and I would not forget to thank them.
I respect and thank Mrs. S. Amutha Rani M.Sc., B.Ed., for
giving me an opportunity to do this project work and providing us
all support and guidance which made me complete the project on
time.
Last but not least I would like to thank my parents who
helped a lot in gathering different information, collecting data and
guiding me from time to time in completing this project.
Thanking you.
G.Priyadharsan
XII STD

4. DECLARATION
I hereby declare that the project work entitled
“Wheatstone bridge” submitted to Sathya Vidyalaya Senior
Secondary School, Pilliyarkulam for the subject of Physics. Under
the guidance of Mrs. Amutha Rani., M.Sc., B.Ed (Physics) is a
record of original workdone by me. I further declare that this project
record or any part of this has not been submitted elsewhere for any
class.
Place:
Date:
Signature of the Candidate

5. CONTENTS
Sl. No. CONTENTS
1 AIM OF THE PROJECT
2 INTRODUCTION
3 THEORY
4 EXPERIMENTATION
5 APPARATUS REQUIRED
6 PROCEDURE
7 OBSERVATIONS
8 CONCLUSION
9 PRECAUTION
10 BIBLIOGRAPHY

6. AIM OF THE PROJECT
The basic aim of the allotted project is to understand
and acknowledge the significance of the ‘Wheatstone
Bridge’ in the field of electricity and the advancements
it unfolded which resulted in direct or indirect progress
in field of scienceand engineering.
Moreover ,it aims at understanding the working of
the Wheatstone Bridge and the mechanism it follows;
the projectalso emphasises on the significance of
Kirchoff’s Laws as well as Ohm’s law in the
Wheatstone Bridge and its derivation; it also spotlights
the efforts of brilliant scientists and physicists whose
constant efforts and hardwork led to the invention of
“Wheatstone Bridge”.
In the end, project discusses about the unignorable
importance wheatstone bridge plays in the social as
well engineering aspects. It also includes an
experimentation withthe aim of calculating the
unknown resistance using a Wheatstone Bridge.

7. R2/R1 = Rx/R3
R2.R3= Rx.R1
INTRODUCTION
A Wheatstone Bridge is aN electrical circuit used to measure an
unknown electrical resistance by balancing two legs of a bridge
circuit, one leg of which includes the unknown resistance.
Its primary operation in a circuit is its property to provide
extremelyaccurate measurement. This characteristics of
a Wheatstone Bridge is often exploited
to calculate resistances of various
electronic devices with minimal
uncertainities . It can also measure
inductance, capacitance, and
frequency with the proper combination
and arrangement of inductances and
capacitancesin its arms. It is an DC
bridge and requires
Direct Current for its working. At the balance condition
the deflection at the centre is null if and only if the
product of thediagnol resistances are found to be equal,
that is :

Or

8. History Of Wheatstone Bridge :
Wheatstone bridge as reflected by the name was
made popular byCharles Wheatstone in 1843. However
the actual credit of its development goes to Samuel
Hunter Christie. The following excerpt discusses the
contributions of both the scientists in the development of
the bridge and the reason behind terming it as
“Wheatstone Bridge” :
Samuel Hunter Christie:
Samuel Hunter Christie was a British mathematician and
physicist born on 22 March,1784 in London. He was a Fellow Of
The Royal Society in 1826. His primary interests were in
studying Earth’s Magnetism and designing improvements to the
magnetic compass. He delivered his Bakerian Lecture in 1833
which was on ” Experimental Determination of the Laws of
Magneto-Electric Induction in different masses of the same
metal, and its intensity in
different metals.” and was awarded with Bakerian
medalfor the same. Christie’s research paper was
a printed version of his Bakerian Lecture for 1833,
it was 50 pageslong; christie used current pulses
inplace of steady currents obtained through
magnetoelectric induction , which was discovered
by Michael Faraday only 15 months earlier.
Christie used long and tedious method
for deriving the relation and his research paper reflects that he
was unfamiliar with the ohm’s law. Moreover, it is evident from
his work that he was unknown to the idea of current running
through the closed loop and believed that the current is created
independently indifferent parts of the circuit. He also finds
correctly that the conducting power is proportional to the cross-
sectional area.
In his paper he published the revolutionary ‘diamond ’ method , the
forerunner of Wheatstone bridge in a paper on magnetic and electrical
properties of metals as a method for comparing resistancesof wires of
different thicknesses. He is credited with proposal of Wheatstone Bridge ,
however his method went unrecognised until 1843 when Charles
Wheatstone proposed it in the Royal Society as a method for measuring
resistances in electrical circuit. Though Charles proposed it as Samuel
Hunter Christies’s invention the bridge was titled after his name.

9. Charles Wheatstone:
Charles Wheatstone was a English scientist born on 6
February,1802 in Barnwood ,England . He was member of
Royal Society in 1836 and was the inventor of many scientific
breakthrough
during the Victorian era which include musical
instrument concertina, stereoscope ,
symphonium
,telegraph. He also measured the speed of
electricity ina conductor. However, Wheatstone
is best known for his contributions in the
development of the Wheatstone Bridge which
was originally invented by Samuel Hunter
Christie.
He popularised the use of the wheatstone bridge and further
simplified it. Unlike Christie, Charles used the steady current
and came to the very same balancing equation. Moreover, from
his research paper it was evident that he had command over
ohm’s law.A parallel evaluation of the two research papers by
Christie and Wheatstone gives a strong impression of the
overwhelming importance of Ohm’s work; this inturn
popularised ohm’s work on electric current. Wheatstone’s
paper was a breakthrough and soon became popular as a
result bridge got the title “Wheatstone Bridge”;sooner or later
his paper was translated into German and French as “Annalen
Der Physik” and “Annales de Chimie et de Physique”
respectively.
Later, the bridge was further worked upon by prominent
scientistslike William Thomson ,Lord Kelvin and James Clerk
Maxwell whose efforts helped in extending the range of the
device.

10. THEORY
Wheatstone bridge is the name given to the combination of
four resistors connected in the form of diamond to give null
deflection atthe centre. The four resistances of the circuit are
referred to as armsof the bridge.
 Construction Of Wheatstone Bridge :
A Wheatstone bridge circuit consists of four arms of
which twoarms consist of known resistances while the
other two consist of an unknown resistance and a
variable resistance or rheostat.The circuit also consists of
an electromotive force source and a galvanometer which
is connected at the centre of the bridge.
The overall construction of a simple Wheatstone bridge
can beillustrated as :
Where :
R1,R3 =Known
Resistances
Rx=Unknown Resistances
R2=Rheostat
G=Galvanometer
E=Electromotive force
source

11. Rx=R2.R3/R
1
 Principle Of Wheatstone Bridge :
The Wheatstone bridge works upon the Principle Of Null
Deflection that is the ratio of their resistances is equal and no
current flows through the central circuit. Under normal conditions
,the bridge is in an unbalanced condition where current flows
through the galvanometer connected at the centre of the bridge.
The bridge is said to be balanced when nocurrent flows though the
galvanometer and it shows zero or null deflection.
 Derivation of Formula For Wheatstone Bridge :
Using Kirchoff’s Junction Rule in the loop
ABCD we get :
I3 -Ix+Ig=0 (i)
I1-I2-Ig=0 (ii)
 Using Kirchoff’s Loop Law in the loopABD
and BCD we get :
I3.R3-Ig.Rg-I1.R1=0
(iii)Ix.Rx-
I2.R2+Ig.Rg=0 (iv)
When the bridge is balanced the galvanometer shows zero
deflection that is Ig=0 then :
For (iii) : I3.R3-0-I1.R1=0 I3.R3=I1.R1 (v)
For(iv): Ix.Rx-I2.R2+0=0 (vi)
Dividing (vi) by (v) :
Ix.Rx / I3.R3=I2.R2/I1.R1
Rx=I2.I3.R2.R3/I1.R1.Ix
From (i) when Ig=0 :
I3=Ix
From (ii) when Ig=0 :
I1=I2
Therefore :

12.  Application Of Wheatstone Bridge :
 The Wheatstone bridge is used for the precise measurement of
low resistance.
 Wheatstone bridge and an operational amplifier are used to
measure physical parameters such as temperature, light, and
strain.
 Quantities such as impedance, inductance, and capacitance can
be measured using variations on the Wheatstone bridge with
much accuracy.
Resistance of some of the materials, such as semiconductors,
tends to vary with the temperature. The variations are large in
comparison to the ordinary resistors. These are known as
thermistors. A slight change in temperatures can be measured
using thermistors for the Wheatstone bridge setup.
 Wheatstone bridge can also be used for measuring strain and
pressure.
 Limitations Of Wheatstone Bridge :
 For low resistance measurement, the resistance of the leads
and contacts becomes significant and introduces an error.
 It is only accurate for measurements of low resistance. If the
unknown resistance has a huge value, then the galvanometer
becomes difficult to balance.
 When the resistance draws a huge current from the circuit, it
displays heating effect. This leads to an inaccurate reading.
 The Wheatstone bridge is a delicate device. In an off-balance
situation, measurements may not even be accurate.
 Wheatstone bridges are commonly used to measure the
resistance of a few ohms to those few kilo-ohms.


13. EXPERIMENTATION
A bridge circuit in its simplest form consists of network
of fourresistance arms forming a closed circuit,
with a dc source of current applied
to two opposite junctions and a
current detector connected to the
other two junctions.
Wheatstone bridge is used for
accurate measurement of
resistance. The circuit diagram of
a typical Wheatstone bridge is
given alongside.
Mentioned below is the experimentation to find the
unknownresistance using a Wheatstone bridge.
Aim Of The Experiment 
To study and perform a experiment to measure the
unknownresistance using Wheatstone bridge.
Apparatus Required 
 Three medium resistors
 DC source
 Galvanometer
 Connecting wires
 Key
 Rheostat

14.  Procedure Followed :
 Measure the resistance of the three known resistors and
connectthem in the form of diamond.
 Connect the Galvanometer
with the terminals of two
resistors and connect theDC
source with the terminals of
the other two resistors.
 Connect the unknown
resistance inseries with
the rheostat.
 Connect key with the
Electromotiveforce
source in the circuit.
 Increase or Decrease the resistance of the rheostat
until theGalvanometer shows null deflection.
 Note down the rheostat’s resistance when
galvanometer showsnull deflection.
Observation
When the circuit is unbalanced a non null deflection is observed inthe
galvanometer. However, on increasing or decreasing the resistance of the
rheostat in such a way that the circuit becomes balanced ,a null deflection is
observed.
Conclusions
At balanced condition, the galvanometer shows null deflection ;
thisinfers that the net current through the galvanometer is zero and
no circulation of current through the galvanometer takes place.
It also infers that the current through the R3 resistors equals the
current through the Rx resistor and the current through the R1
resistor equals current through the R2 resistor.
Thus, at balanced condition the unknown resistance can be
calculated by using the formula :

15. Precautions:
o Make all the connections neat, clean and tight.
o Use a freshly charged battery so that its emf may remain
constantthroughout the experiment.
o While making connections make sure to plug off the key or
openthe key.
o Make sure the connecting wire is of uniform cross-section area.
o Make sure that short circuiting does not takes place.

16. BIBLIOGRAPHY
* www.wikipedia.com
* www.britannica.com
* The Genesis Of Wheatstone Bridge By Stig Ekelof
* www.researchgate.net
*www.atomstalk.com
*https://nationalmaglab.org
*www.semiconductorsforu.com
*www.electrical4u.com
*www.electricaldeck.com
*www.cambridge.org
*www.thoughtco.com
*https://journals.sagepub.com