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Physics Project 1 - DSFDSGSGDFSG
physics class 12 (Delhi Public School, Damanjodi)
Studocu is not sponsored or endorsed by any college or university
Physics Project 1 - DSFDSGSGDFSG
physics class 12 (Delhi Public School, Damanjodi)
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2. PREPARED BY ~ ABHISHEK SINGH
CLASS ~ XII-A
ROLL NO. ~ 05

PHYSICS
PROJECT







TOPIC : WHEATSTONE BRIDGE
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INDEX


S.NO. TOPIC Page No.
1 Certificate Of Excellence 1
2 Acknowledgement 2
3 Aim Of The Project 3
4 Introduction 4-7
5 Theory 8-11
6 Experimentation 12-14

(i)Apparatus Required
12

(ii)Procedure Followed
13

(iii)Observation
13

(iv)Conclusion
13

(v)Precaution
14
7 Bibliography 15

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LUCKNOW PUBLIC SCHOOL
A-BLOCK SOUTHCITY

DEPARTMENT OF PHYSICS


CERTIFICATE

This is to certify that Abhishek Singh ,student of class
XII-A, has successfully completed the research on the
below mentioned project under the guidance of Mr.
Awadesh Kumar Srivastava (Subject Teacher) during
the year 2022-23 in partial fulfilment of Physics
Practical Examination conducted by AISSCE, New Delhi.




Signature Of External Examiner Signature Of Physics Teacher

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ACKNOWLEDGEMENT

In the accomplishment of this project successfully, many
people have bestowed upon me their blessings and their heart
pledged support; in response to which I would like to
acknowledge them for their selfless help and support.
Primarily, I would like to thank my Principal, Ms. Aparna
Tripathi, for being an idol and guiding us through much
needed moral support. Then I would like to thank our
honorable Physics Teacher, Mr. Awadhesh Kumar Srivastava,
for their constant efforts and support which played a major
part in the success of the project.
Moving on,I would like to thank my parents and friends who
have helped me with their valuable suggestions and guidance
which proved to be a great aid in completion of this project .
Last but not the least I would like to thank my classmates who
played an important role in bestowing me with their profound
ideas and knowledge. I am also thankful to all those whose
names are not mentioned above but helped encouraged and
inspired me knowing or unknowing in doing this work.



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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 science
and engineering.
Moreover ,it aims at understanding the working of the
Wheatstone Bridge and the mechanism it follows; the project
also 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 with
the aim of calculating the unknown resistance using a
Wheatstone Bridge.




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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 extremely
accurate 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 capacitances
in 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 the
diagnol resistances are found to be equal, that is :


or


➢ History Of Wheatstone Bridge :
Wheatstone bridge as reflected by the name was made popular by
Charles 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
R2/R1 = Rx/R3
R2.R3= Rx.R1
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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 medal
for the same. Christie’s research paper was a printed
version of his Bakerian Lecture for 1833, it was 50 pages
long; 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 in
different 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 resistances
of 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
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Charles proposed it as Samuel Hunter Christies’s invention the bridge
was titled after his name.

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 in
a 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 scientists
like William Thomson ,Lord Kelvin and James Clerk Maxwell whose
efforts helped in extending the range of the device.
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THEORY

Wheatstone bridge is the name given to the combination of four
resistors connected in the form of diamond to give null deflection at
the centre. The four resistances of the circuit are referred to as arms
of the bridge.

➢ Construction Of Wheatstone Bridge :

A Wheatstone bridge circuit consists of four arms of which two
arms 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 be
illustrated as :
Where :

R1,R3 →Known Resistances
Rx→Unknown Resistances
R2→Rheostat\Variable Resistance
G→ Galvanometer
E→ Electromotive Force Source
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➢ 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 no
current 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 loop
ABD 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 →Ix.Rx=I2.R2 (vi)
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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 :

Or


➢ 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
R1.Rx=R2.R3
Rx=R2.R3/R1
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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.






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EXPERIMENTATION

A bridge circuit in its simplest form consists of network of four
resistance 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 unknown
resistance using a Wheatstone bridge.

Aim Of The Experiment →
To study and perform a experiment to measure the unknown
resistance using Wheatstone bridge.

Apparatus Required →
(i)Three medium resistors
(ii) DC source
(iii)Galvanometer
(iv)Connecting wires
(v) Ke�
(vi)Rheostat
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Procedure Followed →
→ Measure the resistance of the three known resistors and connect
them in the form of diamond.
→Connect the Galvanometer with the
terminals of two resistors and connect the
DC source with the terminals of the other
two resistors.
→ Connect the unknown resistance in
series with the rheostat.
→Connect key with the Electromotive
force source in the circuit.
→ Increase or Decrease the resistance of the rheostat until the
Galvanometer shows null deflection.
→Note down the rheostat’s resistance when galvanometer shows
null deflection.

Observation→
When the circuit is unbalanced a non null deflection is observed in
the 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 ; this
infers that the net current through the galvanometer is zero and no
circulation of current through the galvanometer takes place.
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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 :

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











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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





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