BHOLANANDA PALLI,

AIRPORT ROAD
AGARTALA, TRIPURA (W)
SESSION: 2024-25
SUBJECT: - ENGLISH LANGUAGE (301)

SUBMITTED BY:-
Name: ANIRBAN CHAKRABORTY
Class: XII
Roll No:
 CERTIFICATE
In the Academic year of 2024-25 in the
institution Sri Krishna Mission School. This
is to certify that, the PHYSICS project titled
“To study the variation in potential drop
with length of a wire for a steady
current.” has been successfully completed
by Anirban Chakraborty of Class XII, in the
partial fulfillment of curriculum of Central
Board of Secondary Education (CBSE)
leading to the award of Board Final
Examination.
 ACKNOWLEDGEMENT

I would like to express my sincere gratitude to my

physics teacher Mrs. Poushali Bhattacharjee, Mr.
Chandra Banerjee and Mr. Rajesh Deb for her vital
support, guidance and encouragement, without
which this project would not have come forth.

I would also like to express my gratitude to my

friends and family for their support during the
making of this project.
 Index

 Objective
 Introduction
 Working Principle
 Materials Required
 Theory
 Procedure
 Data Table
 Result
 Precautions
 Sources of Error
 Conclusion
 Bibliography

Objective
The main objective of this project is to study the working
principle of a potentiometer and its use in measuring the
potential difference (voltage) across a component without
drawing any significant current. The potentiometer is a precise
instrument used for accurate measurement of voltage and
comparison of potential differences in electrical circuits.

Introduction
A potentiometer is a variable resistor with three terminals,
often used to measure the potential difference between two
points in a circuit. Unlike a voltmeter, which draws current from
the circuit to measure the voltage, a potentiometer is designed to
measure the potential difference without significantly affecting
the circuit's operation.
The potentiometer is based on the principle that the potential
difference across a uniform wire is proportional to the length of
the wire. By comparing the unknown voltage with a known
reference voltage, a potentiometer can determine the unknown
voltage with high precision.
 Working Principle
The potentiometer works based on the principle of potential
division. When a uniform wire carrying a current is used, the
voltage drop across the wire is directly proportional to the length
of the wire. The relationship can be expressed as:
V= l/L X Vref
Where:
 V is the voltage across a portion of the wire,
 l is the length of the wire segment with the voltage V,
 L is the total length of the wire,
 Vref is the known reference voltage applied across the total
length of the wire.
By adjusting the position of the sliding contact (known as the
jockey or slider), the length l can be varied, allowing the user to
balance the unknown voltage with the reference voltage.
 Materials Required

 Potentiometer wire (usually a long uniform wire)

 Battery (known reference voltage, e.g., 6V or 12V)

 Galvanometer (to detect current flow)

 Key or switch (to control the circuit)

 Jockey or sliding contact

 Ruler or scale (to measure length)

 Connecting wires

 Unknown voltage source (to be measured)

 Two resistors (if needed to adjust current)

 Battery (power source for the potentiometer circuit)

 Theory
A potentiometer consists of a long, uniform wire stretched along
a straight line. The wire is mounted on a wooden or metallic
base, and the ends of the wire are connected to a voltage source
(reference voltage). A sliding contact (the jockey) is moved
along the wire to tap different points. The potential difference
between any two points along the wire is proportional to the
distance between them.
When measuring an unknown voltage, the potentiometer
compares it with a known reference voltage. The unknown
voltage is connected across one of the terminals, and the jockey
is moved along the wire until the galvanometer shows zero
current, indicating the potential drop across the wire matches the
unknown voltage.
Formula for Potentiometer:-
The relationship between the voltage across the potentiometer
wire and the length is given by:
Vunknown / Vref = l/L
Where:
 Vunknown is the unknown voltage,
 Vref is the reference voltage,
 l is the length of the wire corresponding to the unknown
voltage,
  L is the total length of the potentiometer wire.

Procedure
Step 1: Set Up the Potentiometer Circuit

1. Mount the potentiometer wire on a base, ensuring that the

wire is uniform and straight.
2. Connect one end of the potentiometer wire to the positive
terminal of a battery or DC power supply (known reference
voltage).
3. Connect the other end of the wire to the negative terminal
of the battery or power supply.
4. Attach the galvanometer in series with a key or switch that
can control the current.
Step 2: Connect the Unknown Voltage Source

1. Connect the unknown voltage source across the terminals

of the potentiometer wire.
2. Use the jockey to move along the wire until the
galvanometer shows zero current. This is the point where
the voltage drop across the wire is equal to the unknown
voltage.
Step 3: Measure the Length

1. Measure the length l of the wire between the starting point

and the position of the jockey that gives a null reading on
the galvanometer.
2. Use the known reference voltage Vref and the measured
length l to calculate the unknown voltage Vunknown
Step 4: Calculate the Unknown Voltage
Using the formula:
Vunknown / Vref = l/L X Vref

Where:
 l is the length of wire corresponding to the unknown
voltage,
 L is the total length of the potentiometer wire,
 Vref is the known reference voltage.

Data Table
Length of Wire(l) Total Length of Reference Unknown
(cm) Wire(L)(cm) Voltage(Vref )(V) Voltage(vunknown)(V)

50 100 6 3
60 100 6 3.6
70 100 6 4.2
80 100 6 4.8
90 100 6 5.4

Result
The results demonstrate that the potentiometer can measure the
unknown voltage by balancing it against a known reference
voltage. The length of the wire corresponding to the unknown
voltage is proportional to the unknown voltage, confirming the
principle of potential division. The accuracy of the measurement
depends on the uniformity of the wire and the precision with
which the jockey is moved along the wire.

Precautions
 Use a longer potentiometer wire for more precise
measurements.
 Ensure the wire is uniformly stretched to avoid
inconsistencies in the voltage distribution.
 Use a more sensitive galvanometer to detect smaller potential
differences more accurately.

Sources of Error
 Contact resistance: Poor contact at the terminals or jockey
could introduce errors in measurement.
 Wire uniformity: Any variation in the wire's material or
thickness along its length would affect the results.
 Parallax error: Misreading the length of the wire due to
incorrect eye positioning.

CONCLUSION
This experiment demonstrates the working of a potentiometer
and how it can be used to measure the potential difference
(voltage) accurately. The potentiometer is a valuable tool for
comparing voltages with high precision without drawing current
from the circuit. The results confirmed the linear relationship
between the voltage and the length of the wire, supporting the
principles of potential division and Ohm’s Law.
 Bibliography:-
 NCERT PHYSICS TEXTBOOK FOR CLASS XII
 S.L.ARORA PHYSICS Reference book for Class XII
 GOOGLE.com
 YOUTUBE.com

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