PHYSICS INVESTIGATORY PROJECT
EARTH MAGNETIC FIELD’S MAGNETIC FIELD USING TANGENT
GALVANOMETER
Prepared by: Kartik Ranjan
Roll No:
PHYSICS
PROJECT
EARTH MAGNETIC FIELD
Although historically ancient travellers made abundant use of the earth’s magnetic field for the
exploration of the earth, they were ignorant of its origin. In many respects the earth’s magnetic field
exhibits characteristics similar to those of a bar magnet; nonetheless, the mechanisms responsible for
generating each are vastly different. Magnetic field lines appear to originate near the south geographic
pole, i.e. magnetic north pole, and terminate near the north geographic pole, i.e. magnetic south pole. It
is interesting to note that in the vicinity of Wilmington, North Carolina the magnetic field lines enter the
earth at a relatively steep angle. The angle of inclination or dip angle, which is the angle that a compass
needle makes with respect to the plane of the horizon, is approximately 60. In this experiment principles
of magnetostatics and elementary vector analysis are used to determine the earth’s magnetic field in
the vicinity of Wilmington, North Carolina.
Certificate
This is to certify that
KARTIK RANJAN
of
Class XII- B has completed the Physics Project entitled “To
determine Earth Magnetic Field using Tangent
Galvanometer” himself and under my guidance. The progress
of the project has been continuously reported and has been in
my knowledge consistently.
…………….……….
Internal Examiner
…………….……….
…………….……….
External Examiner
…………….……….
Principal
…………….……….
Acknowledgement
I would like to express my sincere gratitude to my Physics teacher,
Mr. KUNDAN KUMAR SINGH for giving us the wonderful opportunity
to do a case study and providing vital support, guidance and
encouragement throughout the project. Without his motivation and
help, the successful completion of this project would not be possible.
Secondly I would also like to thank my friends who helped me a lot in
finalizing this project within the limited time frame.
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TABLE OF CONTENTS
Overview................................................................................................................................................ 5
Aim of the Project .................................................................................................................................. 5
Apparatus and Materials required .......................................................................................................... 6
Theory ................................................................................................................................................... 7
Applications .................................................................................................................................... 8
Procedure .............................................................................................................................................. 8
The initial ADJUSTMENTS .............................................................................
Procedure for performing simulator ................................................................................................. 9
To determine the horizontal component of earth’s magnetic field (Bh) .......................................... 10
To determine the reduction factor of T.G ...................................................................................... 10
From graph ................................................................................................................................... 11
Result .................................................................................................................................................. 11
Facts............................................................................................................................................. 11
Applications ......................................................................................................................................... 11
Bibliography ......................................................................................................................................... 12
The Tangent galvanometer .................................................................................................................. 12
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OVERVIEW
The tangent galvanometer was first described in an 1837 by Claude-Servais- Mathias Pouillet, who later
employed this sensitive form of galvanometer to verify Ohm’s law. To use the galvanometer, it is first set
up on a level surface and the coil aligned with the magnetic north-south direction. This means that the
compass needle at the middle of the coil is parallel with the plane of the coil when it carries no current.
The current to be measured is now sent through the coil, and produces a magnetic field, perpendicular
to the plane of the coil and is directly proportional to the current.
The magnitude of the magnetic field produced by the coil is B; the magnitude of the horizontal component
the Earth’s magnetic field is B’. the compass needle aligns itself along the vector sum of B and B’ after
rotating through an angle Ø from its original orientation. The vector diagram shows that tan
Ø = B/B’. since the magnetic field of the Earth is constant, and B depends directly on the current, the
current is thus proportional to the tangent of the angle through which the needle has turned.
AIM OF THE PROJECT
The aim of the project is to find the ‘reduction factor’ of the given tangent galvanometer (K) and
the horizontal component of the Earth’s magnetic field (BH).
o To determine the reduction factor of the given tangent galvanometer (K).
o To find out the horizontal component of earth’s magnetic field (Bh).
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TangentgalvanometermadebyJ.H. BunnellCo.around1890
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APPARATUS AND MATERIALS REQUIRED
o Tangent galvanometer (TG),
o commutator (C),
o rheostat (R),
o battery (E), o
ammeter (A), o
key (k), etc. o
Tangent Galvanometer
Battery Eliminator
a) Rotor view
Plug Key
b) Ordinary view
Rheostat
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When a bar magnet is suspended in two Magnetic fields B and Bh, it comes to rest making an angle
θ with the direction of Bh.
THEORY
Tangent galvanometer is an early measuring instrument for small electric currents. It consists of a coil
of insulated copper wire wound on a circular non-magnetic frame. Its working is based on the principle
of the tangent law of magnetism. When a current is passed through the circular coil, a magnetic field
(B) is produced at the centre of the coil in a direction perpendicular to the plane of the coil. The TG is
arranged in such a way that the horizontal component of earth’s magnetic field (Bh) is in the direction of the
plane of the coil. The magnetic needle is then under the action of two mutually perpendicular fields.
If θ is the deflection of the needle, then according to tangent law,
Let I is the current passing through the coil of radius a with n turns, then the field generated by the
current carrying circular coil is,
Equating (1) and (2), we get,
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The left hand side of equation (4) is a constant and is called the reduction factor (K) of the
given tangent galvanometer.
Now from equation (3) & (5), the horizontal intensity of earth’s magnetic field Bh is,
APPLICATIONS
o
T.G can be used to measure the magnitude of the horizontal component of the geomagnetic
field.
o The principle can be used to compare the galvanometer constants.
PROCEDURE
Connections are made as shown in the figure given below, where K is the key, E the battery, A the
ammeter, R the rheostat, C the commutator, and T.G the tangent galvanometer. The commutator can
reverse the current through the T.G coil without changing the current in the rest of the circuit. Taking the
average of the resulting two readings for deflection averages out, any small error in positioning the
TG coil relative to the earth’s magnetic field Bh .
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PROCEDURE FOR PERFORMING EXPERIMENT
1. The plane of the coil is made vertical by adjusting the levelling screws.
2. The compass box alone is rotated so that the 90-90 line in the compass box is in the plane of the
coil.
3. The T.G as a whole is rotated till the Aluminium pointer reads 0-0.
4. Note down the number of turns in the coil.
5. A suitable current is allowed to pass through the coil.
6. Note down the current as well as the deflection in T.G.
7. Reverse the current and note the deflection again.
8. Repeat the procedure for different values of current.
9. Plot the graph.
10. Measure the radius of the coil from its perimeter by using a thread and rotating it around the
round circle.
11. Determine the reduction factor and horizontal intensity of earth's magnetic field.
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TO DETERMINE THE HORIZONTAL COMPONENT OF EARTH’S MAGNETIC FIELD (BH)
The Horizontal component of earth's magnetic field (Bh) can be calculated using the formula,
TO DETERMINE THE REDUCTION FACTOR OF T.G
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1
0.15
56
56
60
60
58
1.6003
0.13
2
0.18
62
62
66
66
64
2.0503
0.18
3
0.22
67
67
71
71
69
2.6059
0.22
4
0.26
70
70
74
74
72
3.0777
0.26
FROM GRAPH
Reduction factor K of the tangent
galvanometer can be determined
From the graph drawn as,
RESULT
The reduction factor of the given tangent galvanometer, K =...19.75.........A
Horizontal component of earth’s magnetic field, Bh =...........T
FACTS
  The tangent galvanometer is an early measuring instrument for Current









The magnetic field produced by a circular coil carrying current I is Proportional to I
The S.I unit of magnetic field is Tesla


The magnitude of horizontal intensity of earth’s magnetic field is3.5x10⁻⁵ T
For better result while
 doing tangent galvanometer experiment, the deflection should be
in between 30-60
What is the value of µ₀ ? 4πx10⁻⁷ NA⁻²
APPLICATIONS



T.G. 
can be used to measure the magnitude of the horizontal component of the geomagnetic
field.
The principle can be used to compare the galvanometer constants.

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BIBLIOGRAPHY




Tangent Galvanometer (Procedure) : Electricity
& Magnetism Virtual Lab : Physical Sciences :

Amrita Vishwa Vidyapeetham Virtual Lab
Tangent Galvanometer (Theory) : Electricity
 & Magnetism Virtual Lab : Physical Sciences :
Amrita Vishwa Vidyapeetham Virtual Lab

Tangent
Galvanometerhttp://physics.kenyon.edu/EarlyApparatus/Electrical_Measurements/Tangent_Gal


van ohmmeter/Tangent_Galvanometer.html


Galvanometer - Wikipedia, the free encyclopedia en.wikipedia.org/wiki/Galvanometer
THE TANGENT GALVANOMETER
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