Potentiometer

1. POTENTIOMETER
Electric circuits
For the partial fulfillment of physic course class XII
Department of Physics
Nepal Mega College
Babarmahal, Kathmandu
Group Members
Prabin Joshi
Prekshya Dhakal
Prenka Oli
Date of submission: 2080/10/20

2. Definition
• The word ‘potentiometer’ is the combination of
potential difference and metering.
• The potentiometer is an instrument used to
measure the unknown voltage by comparing it
with the known voltage.
• It can be used to determine the emf and internal
resistance of the given cell and also used to
compare the emf of different cells.
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3. Types of Potentiometers
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4. Working Principle of Potentiometer
• The basic principle of the potentiometer is that the
potential drop across any section of the wire will
be directly proportional to the length of the wire,
provided the wire is of a uniform cross-sectional
area and a uniform current flows through the wire.
• If V be the p.d across a conductor of length l, then ,
V∝ l
or, V = K.l
or, K =
𝑉
𝐿
where, K is a constant known as a potential
gradient.
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5. CONSTRUCTION
• A long resistance wire of length varying
from 1m to 10m stretched horizontally
between two points A and B.
• A meter scale fitted over a wooden plank.
• A steady current is maintain in the wire by
a cell connected across A and B which is
known as standard cell.
• As a result, there is a p.d between to points
on the wire which is proportional to their
distance from one another.
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6. Applications
1. Comparison of emfs of two cell
2. Measurement of internal resistance of the cell
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7. 1. Comparison of emfs of two cell
• The potentiometer can be used to compare the emf of
two cells of emf ε1 and ε2.
• Let C be the null point when cell ε1 is connected, and
let ‘l1’ be the length between the end A of the wire to
the null point C. Then, the potential difference
between A and C is
• VA – Vc = K.l1 = ε1 ———-(1)
• Let D be the null point when the cell ε2 is connected,
and let ‘l2’ be the length between the end A of the
wire to the null point D. Then, the potential difference
between A and D is
• VA – VD = K.l2 = ε2 ————(2)
• Comparing (1) and (2), we get
• ε1 / ε2 = l1/l2 7

8. 2. Measurement of internal resistance of the
cell
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To determine the internal resistance, the cell
whose internal resistance has to be
determined is connected across the
resistance box (R.B) through the key(K2).
When the K2 key is open, the null point is
obtained at a distance lAc from A. Then,
E1 = K.lAC ——-(1)
When the K2 key is closed, a current ‘i’ is
passed through the resistance box (R). Let
the null point be at a distance of lAD from A.
Therefore, the potential difference will be
v = K.lAD ——–(2)

9. Comparing (1) and (2), we get
ε/v = lAC/lAD ———(3)
We know ε = i(r+R) and v = iR
Therefore, equation (3) becomes
[i(r+R)/ iR] = lAC/lAD
Therefore, internal resistance,
r = R
lAC−lAD
lAD
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10. Potentiometer Sensitivity
• The sensitivity of the potentiometer is the slightest change in the
potential difference that a potentiometer can measure. The sensitivity
of the potentiometer can be increased by decreasing the potential
gradient, i.e., by increasing the length of the potentiometer wire.
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11. Application
1. Volume Controls in Audio Systems
2. Brightness Controls in Displays
3. Tuning Controls in Radios
4. Sensing and Control in Robotics
5. Voltage Dividers and Signal Scaling
6. Dimmer Switches for Lighting
7. Educational Demonstrations
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12. Conclusion
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• Potentiometer's significance lies in its adaptability and functionality.
• It’s applications span a broad spectrum of electronic systems.
- Educational settings or sophisticated control systems
• A cornerstone in the world of electronics

13. Acknowledgement
• We would like to express our profound gratitude to Nepal Mega
College and the Department of physics for providing us with the
invaluable opportunity to undertake this study. Our heartfelt thanks
extend to our respected teachers of physics for this opportunity.
• Last, but certainly not least, We extend our heartfelt thanks to our
families, whose unwavering belief in us and constant encouragement
have been the driving force behind our pursuit of academic excellence
and personal growth. Their support has been our pillar of strength
throughout this journey.
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14. References
1. The Authoritative Dictionary of IEEE Standards Terms (IEEE
100) (seventh ed.). Piscataway, New Jersey: IEEE Press. 2000. ISBN 0-
7381-2601-2.
2. "Resistor Guide". Retrieved 3 January 2018.
3. Elliot, Rod. "Beginners' Guide to Potentiometers". Elliott Sound Products.
Retrieved 7 June 2012.
4. Peterson, Phillip. "Linear Type Precision Potentiometer
Diagram" (PDF). Precision Sensors. Betatronix. Retrieved 29 April 2015.
5. "Potentiometer taper". the Resistor Guide. Retrieved 19 November 2012.
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15. References
6. Jhakki, Akki (2020). Concise Physics Class IX (ICSE). New Delhi:
Selina Publishers Pvt. Ltd. p. 189. ISBN 9789388594387.
7. Brian Bowers (ed.), Sir Charles Wheatstone FRS: 1802-1875, IET,
2001 ISBN 0-85296-103-0 pp.104-105
8."stat". Oxford English Dictionary (Online ed.). Oxford University
Press. (Subscription or participating institution membership required.)
9. Koirala, R. P., & Khanal, P. (2080). Principles of Physics Grade XII.
Asmita Books Publisher and Distributors (P) Ltd.
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