2. CERTIFICATE
This is to certify that ,I Vaibhav Pandey, a student of class
XII Science has successfully completed the project under
the guidance of Mr. Ramkesh Verma (P.G.T Physics) during
the academic year 2022-23 in partial fullfilment of Physics
practical examination conducted by CBSE.
Signature of External Examiner Signature of Principal
Signature of Physics Teacher
3. ACKNOWLEDGEMENT
5 January 2023
In the accomplishment of this project successfully, many people have best owned
upon me their blessings and the heart pledged support, this time I am utilizing to
thank all the people who have been concerned with this project.
Primarily, I would like to thanks god for being able to complete this project with
success. Then I would like to thank my principal Mr. Mayank Kumar Srivastava and
my physics teacher Mr. Ramkesh Verma, whose valuable guidance has been the
ones that helped me to patch this project and make it full proof success, his
suggestions and his instructions has served as the major contributor towards the
completion of this project.
Then I would like to thank my parents and friends who have helped me with their
valuable suggestions and their guidance has been very helpful in various phases of
the completion of this project.
4. AIM
To study the construction and
application of Wheatstone
bridge.
5. CONTENT
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1. Introduction
2. Components of Wheatstone Bridge
3. Circuit Construction
4. Working principle of Wheatstone Bridge
5. Example Circuit
6. Applications of Wheatstone Bridge
7. Limitations of Wheatstone Bridge
8. Summary
9. Bibliography
10. Precautions
6. INTRODUCTION
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Samuel Hunter Christie invented the Wheatstone bridge in
the year 1833, which became popular with the works of Sir
Charles Wheatstone in 1843. An electrical circuit that is set
up to measure the unknown value of a resistor and creates
a balance between the two legs of the bridge circuit is
called a Wheatstone Bridge. As shown in the figure below,
three resistances are known (one is variable / adjustable )
and the fourth one has to be found out. Compared to the
other measuring instruments such as voltage divider, the
concept of Wheatstone bridge is widely used because of
the accuracy in its measurement of resistance.
7. COMPONENTS OF WHEATSTONE BRIDGE
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A resistor with an unknown resistance value.
Two resistors (with known resistance value)
Variable Resistor (a device like .
Rheostat or Preset could workk) Voltage/DC source
Galvanometer (or any device which indicates the
voltage difference or the
Connecting wire.
Circuit Construction.
Construction of Wheatstone Bridge.
9. CIRCUIT CONSTRUCTION
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A Wheatstone bridge is a bridge-type
structure having four resistors, three of
Known and one or unknown value. Here
R1, R2, and R3 have known values among
which R2 is adjustable and finally Rx is the
value to be measured. Along with these
resistances, a galvanometer
(Vg) is there between B & D, and a DC
supply between A & C.
10. WORKING PRINCIPLE OF WHEATSTONE
BRIDGE
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Now according to the Wheatstone bridge principle if the ratio of
the two resistances (R1/R2) on one edge is equal to the ratio of
the two resistance (R3/Rx) on another edge then there will be no
flow of current between the midpoints of the two edges of
resistance. This condition of the bridge is known as the Balanced
Bridge Condition.
In the Balanced Bridge condition, the current through the
galvanometer is zero and also the voltage difference between
the points B & D becomes zero, i.e. at both points voltage
level would be the same.
Writing equations for the balanced bridge condition would look
like:
R1/R2 =R3/Rx --> R1 X Rx =R2 X R3
11. WORKING PRINCIPLE OF WHEATSTONE
BRIDGE
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Thus, Rx = R3 * (R2/R1)
This detection of zero current in galvanometer is of high
precision, thus depending on the level of precision of
known values, the unknown resistance can be found
with the highest rate of accuracy and precision.
In the Wheatstone bridge experiment, one resistor
should always be variable in order to obtain a balanced
condition. The Circuit performs at its best when the
regulated voltage source is used, instead of the current
with repelling characteristics.
12. EXAMPLE CIRCUIT
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Let us consider the below circuit
where the bridge is in an unbalanced
conditi -on and we need to calculate
the voltage difference between Q1
and Q2, i.e., Volt and hence the value
of R4 needed to make the bridge
balanced
14. Example of Wheatstone Bridge
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As per the voltage division law, Vq1 = (R3/(R3+R1)) * Vs ,
where Vs= 100volts (voltage source)
Putting values of R3 =40Ω, R1=50Ω, and Vs= 100
volts, we get Vq1 = 44.4 volts Similarly, Vq2 = (R4/(R4+R2)) * Vs
putting the values, R4 =50Ω, R2=100Ω, and Vs =100
volts, we get Vq2 =33.3 volts
Thus, Volt can be found as, Volt = Vq1 - Vq2 So, Volt = 44.4 -33.3= 11.1 volts
Now to make the bridge balanced, we can find a suitable value for R4 as done below: R4
R2 * (R3/R1)
putting the values of R1, R2, and R3, we have
R4 =100 * (40/50)=80 volts
Therefore, R4 = 80 volts is the value of resistor which
should be used to make the bridge in a balanced condition.
15. APPLICATIONS OF WHEATSTONE BRIDGE
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Used in Light detecting devices.
For measuring the changes in the pressure.
For measuring the changes in the strain of the
circuit.
Used for the Sensing of mechanical and electrical
quantities.
Also, photo resistive devices use this circuit.
Thermometers also use Wheatstone bridges for the
temperature measurements which need to be
accurate.
Values like capacitance, inductance, impedance, etc.
can be measured with some variations in the
Wheatstone bridge circuit
16. LIMITATIONS OF WHEATSTONE BRIDGE
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Along with all these advantages, there are a few
limitations of the Wheatstone bridge as well, such as:
Readings may be inaccurate under unbalanced
conditions.
The range of measured resistance varies from a few
ohms to mega ohms.
Susceptibility for high dc current is not there.
17. SUMMARY
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Created in 1833, popularized in 1840s.
Wheatstone bridges are one of the best methods of
measuring resistance due to the basic mathematical
ratio involved.
Accurate standards with sensitive enough voltmeter,
measurements of resistance within .05% can be
reached.
Many calibration laboratories still use this method
today.
The Wheatstone Bridge are replaceable; however, for its
simplicity and versatility the circuit is an indispensible
piece of technology.
18. BIBLIOGRAPHY
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Websites :-
www.go0gle.com
www.wikipedia.com
www.youtubecom
Books :-
NCERT CLASS 12th Physics
PRACTICAL Physics Class 12th
19. PRECAUTIONS
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Clean the connecting wires
properly.
Hold the jockey perpendicular
to the wire.
All connections should be neat
and tight.
