VELAMMAL VIDHYASHRAM
SURAPET
PHYSICS INVESTIGATORY PROJECT
ON
To study the earth's magnetic field using a compass needle bar magnet by plotting magnetic field lines and tangent
galvanometer.
NAME : k dinesh subramaniam
CLASS : 12 b2
ROLL NUMBER :
SSCE -2023 -2024
CERTIFICATE
This is to certify that, K Dinesh Subramaniam of class 12B2 has successfully
completed the project on the topic To study the earth's magnetic field using a
compass needle -bar magnet by plotting magnetic field lines and tangent
galvanometer.under the guidance of Ms Nishanthi D in partial fulfillment of
physics practical examination conducted by SSCE, CBSE, New Delhi for the
academic year 2023 – 2024.
Signature of teacher in charge
Signature of Principal
Signature of Internal Examiner
Signature of External Examiner
ACKNOWLEDGEMENT
In the accomplishment of this project successfully, many people have best owned
upon me their blessings and the heart pledged support. So I am utilizing this
opportunity to thank all the people who have been concerned with my project.
Primarily I would like to thank God almighty for giving me the strength,
knowledge and good health to complete this project with success.
Then I would like to thank our Principal sir for his continuous support and our
physics teacher whose whole hearted guidance helped me to patch this project
and make it full proof success. The suggestions and instructions given by them
served as the major contribution to the completion of this project.
Then I would like to thank my parents and friends who have helped me with their
valuable suggestions and guidance, which has been helpful in various phases of
the completion of this project.
Last but not the least I would like to thank my classmates who have helped me a
lot.
TABLE OF CONTENTS
1.Overview
2.Aim of the Project
3.Apparatus and Materials required
4.Theory
5.Procedure
6.Observations and Graph
a. To determine the horizontal component of
earth’s magnet
b. Field (H)
c. From graph
7.Result
8.Precautions
9.Sources of error
10. Facts
11. Applications
12. Bibliography
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 study the Earth’s magnetic field and
find its value (BH) using a tangent galvanometer.
Tangent galvanometer made by
galvanometer
J.H. Bunnell Co. around 1890.
1950.
Topview of a tangent
APPARATUS AND MATERIALS REQUIRED
•
•
•
•
•
Tangent Galvanometer (TG),
Commutator (C),
Rheostat (R),
Battery (E),
Ammeter (A),
made about
• Key (K), etc
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 working of tangent galvanometer is based on the tangent
law. It is stated as when a magnet is suspended freely in magnetic field F
and H, the magnet comes to rest making an angle θ with the direction H
such that,
F = H tan θ
(1)
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.
…………..7
Let a current I be passed through the coil of radius R, having turns N.
Then magnetic field produced at the centre of coil is,
μ 2πIN
𝐹 = 4π0
(2)
𝑅
Let H is the horizontal component of earth’s magnetic field and the
magnetic needle comes to rest at angle 𝜃 with the direction of H, then
according Eq. (1),
μ 2πIN
𝐻𝑡𝑎𝑛𝜃 = 4π0
𝑅
−7
𝐻𝑡𝑎𝑛𝜃 = 10
𝐻=
2πIN
𝑅
2π×10−7 IN
(3)
𝑅𝑡𝑎𝑛𝜃
by substituting the value of current I , from eq. (3),
𝑡𝑎𝑛𝜃
𝐼
𝜇
= ቀ4𝜋0 ቁ
2𝜋𝑁
𝑅𝐻
(4)
radius of coil of galvanometer R, deflection 𝜃 and N, the value of H can
be calculated.
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 H .
PROCEDURE FOR PERFORMING THE EXPERIMENT
1. Make the circuit connections in accordance with the circuit diagram.
2. Using spirit level, level the base and the compass needle in compass
box of tangent galvanometer by adjusting the leveling screw.
3. Now rotate the coil of the galvanometer about its vertical axis, till
the magnetic needle, its image in the plane mirror fixed at the base
of the compass box and the coil, i.e. all
4. these three lie in the same vertical plane. In this setting,
5. the ends of the aluminium pointer should read zero-zero. If this is not
so, rotate the box without disturbing the position of the coil till at
least one of the ends of the pointer stands at the zero marks.
6. By closing the key K, the current flow in the galvanometer. Read the
both ends of the pointer. Now reverse the direction of current by
using the reversing key. When the mean values of both deflections
shown by the pointer in the two cases (i.e. before and after reversing
the current) differ by more than 1o, then turn slightly the vertical coil
until the two values agree. This will set the plane of the coil exactly
in the magnetic meridian.
7. By adjusting the rheostat, bring the deflection in galvanometer
around 45o. The deflection should not be outside the range (30o-60o).
8. Record the reading of the ammeter and the deflection of the compass
needle in the box shown by two ends of pointer on the scale.
9. Reverse the current in the coil of galvanometer and again record the
current and deflection of needle.
10.
By changing the value of current, take four or more set of
readings and plot the graph between I and tan𝜃. The graph will be a
straight line.
11.
Measure the inner and the outer diameter of the coil with a half
metre scale at least three times.
OBSERVATIONS
1. Range of the Ammeter –
2. Least count of Ammeter –
3. Zero error in Ammeter –
4. Number of turns used (N) –
Table 1. For variation of 𝜽 with I
S.No.
1.
2.
3.
4.
5.
Value of deflection,
Mean tan θ
θ (degree)
For direct
For reverse
current
current
θ1
θ2
θ3
θ4
35
35
35
35
35
0.70
49
47
60
64
53.6 1.36
36
36
55
58 46.25 1.04
50
50
65
68
58.2 1.61
45
45
64
65
53.8 1.37
Ammeter
reading
(A)
Obs Corrected
0.15
0.15
0.20
0.20
0.25
0.25
0.30
0.30
0.27
0.27
Table 2. For radius of tangent Galvanometer
S.No.
1.
2.
Inner
diameter d1
(cm)
16.0
× 10−2
Outer diameter Mean diameter Mean radius
d2 (cm)
d
(cm)
16.40 × 10−2 16.20 × 10−2
16.08 × 10−2
16.12 × 10−2
8.10 ×
10−2
3.
16.16
× 10−2
16.10 × 10−2 16.08 × 10−2
8.06
× 10−2
8.04
× 10−2
16.06
× 10−2
Mean radius of coil R = 8.04 × 10−2
GRAPH
Slope of straight line =
BC
AC
m=
tanθ
I
Now substitute the m in Eq. (4),
μ0 2πN
m = 4π
RH
Then, H = 7.6867 × 10−8 𝑇
RESULT
The value of earth’s magnetic field by using a tangent galvanometer is
H = 7.6867 × 10−8 𝑇
PRECAUTIONS
1. The battery should be freshly charged.
2. The magnetic needle should swing freely in the horizontal plane.
3. The plane of coil must be set in magnetic meridian.
4. There should be no parallax in noting down the readings of ammeter
and deflection.
5. All the readings should be adjusted between 30o and 60o.
SOURCES OF ERROR
1. There may a magnetic material around apparatus.
2. The plane of coil will not be exactly in the magnetic meridian.
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 30o-60o.
➢ The value of μ₀ is 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.
➢ For calibration of secondary instruments.
BIBLIOGRAPHY
➢ Tangent Galvanometer (Procedure) :Comprehensive Physics
Activities Volume I : Laxmi Publications Pvt Ltd.
➢ Tangent Galvanometer (Theory) : Comprehensive Physics
Activities Volume I : Laxmi Publications Pvt Ltd.
➢ Tangent Galvanometer (Precautions and Sources of error) :
Comprehensive Physics Activities Volume I : Laxmi Publications
Pvt Ltd.
➢ Galvanometer:
http://physics.kenyon.edu/EarlyApparatus/Electrical_Measurement
s/Tangent_Galvanometer/Tangent_Galvanometer.html
➢ Galvanometer: Wikipedia, the free encyclopedia
en.wikipedia.org/wiki/Galvanometer