PHYSICS INVESTIGATORY REPORT
EARTH MAGNETIC FIELD’S MAGNETIC FIELD USING TANGENT
GALVANOMETER
Prepared by: Amit sh (XII-B/A/C )
Roll No:
PHYSICS
INVESTIGATORY
REPORT
EARTH MAGNETIC FIELD
Although historically ancient travelers 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
A tangent galvanometer
is an early measuring
instrument used for the
measurement of electric
current. It works by using
a compass needle to
compare a magnetic field
generated
by
the
unknown current to the
magnetic
field
of
the
Earth. It gets its name
from
its
operating
principle, the tangent law
of
magnetism,
which
states that the tangent of
the angle 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.
needle
makes
is
proportional to the ratio
of the strengths of the
two
perpendicular
magnetic fields. It was
first described by Claude
Pouillet
later
in
1837.Who
employed
sensitive
form
this
of
galvanometer to verify
Ohm’s law.
1
Amit sh | Vanasthali public School | XII- B/A/C
vanasthali public School
Vasundhara, Ghaziabad
Certificate
2016-17
This is to certify that Amit of Class XII-B/A/C 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
2
Amit sh | Vanasthali public School | XII- B/A/C
…………….……….
External Examiner
Acknowledgement
I would like to express my sincere gratitude to my Physics teacher,
Mr. Nitin Jassal 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.
3
Amit sh | Vanasthali public School | XII- B/A/C
TABLE OF CONTENTS
Overview................................................................................................................................................ 5
Aim of the Project .................................................................................................................................. 5
Apparatus and Materials required .......................................................................................................... 6
Theory ................................................................................................................................................... 7
Applications .................................................................................................................................... 8
Procedure .............................................................................................................................................. 8
The initial ADJUSTMENTS .............................................................. Error! Bookmark not defined.
Procedure for performing simulator ................................................................................................. 9
Observations and Graph ...................................................................................................................... 10
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
4
Amit sh | Vanasthali public School | XII- B/A/C
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
o
To determine the reduction factor of the given tangent galvanometer (K).
To find out the horizontal component of earth’s magnetic field (Bh).
Topviewofa
tangentgal
vanometer
madeabout
1950.Thein
dicatornee
dle
ofthecomp
assisperpen
diculartoth
eshorter,bl
ackmagnet
icneedle.
TangentgalvanometermadebyJ.H. BunnellCo.around1890
5
Amit sh | Vanasthali public School | XII- B/A/C
APPARATUS AND MATERIALS REQUIRED
o
o
o
o
o
o
o
Tangent galvanometer (TG),
commutator (C),
rheostat (R),
battery (E),
ammeter (A),
key (k), etc
Tangent Galvanometer
Battery Eliminator
Plug Key
a) Rotor view b) Ordinary view
Rheostat
6
Amit sh | Vanasthali public School | XII- B/A/C
When a bar magnet is suspended in two Magnetic fields B and Bh, it comes to rest making an angle θ
with the direction ofBh.
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 center 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,
7
Amit sh | Vanasthali public School | XII- B/A/C
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
o
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.
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 .
8
Amit sh | Vanasthali public School | XII- B/A/C
PROCEDURE FOR PERFORMING EXPERIMENT
1. The plane of the coil is made vertical by adjusting the leveling 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 currrent 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.
9
Amit sh | Vanasthali public School | XII- B/A/C
OBSERVATIONS AND GRAPH
Number of turns in the coil =....
Circumference of the coil,
=......cm
Radius of the coil, a =....cm
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
10
Amit sh | Vanasthali public School | XII- B/A/C
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 =............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.
11
Amit sh | Vanasthali public School | XII- B/A/C
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 ometer/Tangent_Galvanometer.html
 Galvanometer - Wikipedia, the free encyclopedia en.wikipedia.org/wiki/Galvanometer
THE TANGENT GALVANOMETER
12
Amit sh | Vanasthali public School | XII- B/A/C
13
Amit sh | Vanasthali public School | XII- B/A/C
14
Amit sh | Vanasthali public School | XII- B/A/C