.
1
SRI SESHAAS INTERNATIONAL PUBLIC
SCHOOL
SESSION : 2019 – 20
PROJECT: T o s t u d y t h e e a r t h ' s m a g n e t i c f i e l d
using a compass needle -bar magnet by
plotting magnetic field lines and tangent
galvanometer.
Submitted to :
MR. SUVENDU DASH
Submitted by:
SREE NAVANEETHA KANNA S
Roll No:
2
This is to certify that
Mr.
a student of class 12th
has
of
submitted a project
report entitled “
” successfully under my guidance and supervision.
Internal Examiner
External Examiner
Principal
3
I wish to express my deep gratitude and sincere thanks to the
Principal, Mỉs. Sailaja, Sỉi ScsKaas Inīcỉnaīional ‫ק‬u"lic ScKool for
her encouragement and for all the facilities that she provided for this
project work. I sincerely appreciate this magnanimity by taking me
into her fold for which I shall remain indebted to her. I extend my
hearty thanks to Mr. Yaseen Shaik , physics teacher, who guided me
to the successful completion of this project. I take this opportunity to
express my deep sense of gratitude for his invaluable guidance,
constant encouragement, constructive comments, sympathetic
attitude and immense motivation, which has sustained my efforts at
all stages of this project work.
SREE NAVANEETHA KANNA S
Class XII
4
S.No
Topic
Page No
1
Aim
5
2
Introduction
6-10
3
Applications
10
4
Apparatus and Materials required
11-12
5
Theory
13-14
6
Procedure
14-16
7
Observation and Calculation
16-17
8
Graph and Result
17-18
9
Precautions
18
10
Facts
19
11
Bibliography
20
5
AIM
The aim of the project is to study the Earth’s magnetic field and find its
value (BH) using a tangent galvanometer.
Tangent galvanometer
Top view of a Tangent galvanometer
6
INTRODUCTION
Earth's magnetic field, also known as the geomagnetic field, is the
magnetic field that extends from the Earth's interior to where it meets the
solar wind, a stream of charged particles emanating from the Sun. Its
m
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en
y
tilted at an angle of about 10 degrees with respect to Earth's rotational
axis, as if there were a bar magnet placed at that angle at the center of the
Earth. Unlike a bar magnet, however, Earth's magnetic field changes over
time because it is generated by a geodynamic (in Earth's case, the motion
of molten iron alloys in its outer core).
The North and South magnetic poles wander widely, but sufficiently
slowly for ordinary compasses to remain useful for navigation. However,
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switch places. These reversals of the geomagnetic poles leave a record in
rocks that are of value to paleomagnetists in calculating geomagnetic
fields in the past. Such information in turn is helpful in studying the
motions of continents and ocean floors in the process of plate tectonics.
The magnetosphere is the region above the ionosphere and extends several
tens of thousands of kilometers into space, protecting the Earth from the
charged particles of the solar wind and cosmic rays that would otherwise
strip away the upper atmosphere, including the ozone layer that protects
the Earth from harmful ultraviolet radiation.
Earth's magnetic field serves to deflect most of the solar wind, whose
charged particles would otherwise strip away the ozone layer that protects
the Earth from harmful ultraviolet radiation. One stripping mechanism is
for gas to be caught in bubbles of magnetic field, which are ripped off by
solar winds.
The intensity of the field is often measured in gauss (G), but is generally
reported in nanoteslas (nT), with 1 G = 100,000 nT. A nanotesla is also
referred to as a gamma (γ).The tesla is the SI unit of the Magnetic field, B.
7
The field ranges between approximately 25,000 and 65,000 nT (0.25–0.65
G).
Near the surface of the Earth, its magnetic field can be closely
approximated by the field of a magnetic dipole positioned at the center of
the Earth and tilted at an angle of about 10° with respect to the rotational
axis of the Earth. The dipole is roughly equivalent to a powerful bar
magnet, with its South Pole pointing towards the geomagnetic North Pole.
The north pole of a magnet is so defined because, if allowed to rotate
freely, it points roughly northward (in the geographic sense). Since the
north pole of a magnet attracts the south poles of other magnets and repels
the north poles, it must be attracted to the South Pole.
8
TANGENT GALVANOMETER
Principle
The tangent galvanometer works on the principle of tangent law.
Tangent law of Magnetism
•
The tangent law of magnetism states that the tangent of the angle of
a compass needle which is due to the movement under the influence
of magnetic field is directly proportional to the ratio of strengths of
two perpendicular magnetic fields.
9
•
In simpler words, the tangent of the angle made by the moving
needle under the magnetic field directly indicates the strength of the
perpendicular magnetic fields.
Definition
•
Tangent galvanometer is the device which was used to measure
small amounts of electric current.
Construction
•
•
•
The working of tangent galvanometer is based on the principle of
tangent law of magnetism.
It consists of a coil of insulated copper wire wound on a circular
non-magnetic frame.
It is utmost necessary that the coil wound is done in helical
arrangement otherwise, the field due to the wire will affect the
compass needle, thus inducing an error in the reading.
•
•
•
This frame is mounted vertically on a horizontal base for support.
The coil of insulated copper wire is usually rotated on a vertical axis
passing through its centre.
A small sized magnetic compass with a powerful magnetic needle is
made to pivote at the centre of this coil, such that it is free to rotate
in a horizontal plane.
10
•
•
The circular scale is used to read the movement of this magnetic
needle which is divided into four quadrants, each ranging from 0° to
90°.
A pointer is attached to this needle at right angles, usually made up
of thin alluminium as alluminium is lighter in mass.
•
The usual way of discarding possibilities of parallax is also used i.e
placing of a plane mirror below the compass needle.
Working
•
The instrument needle starts moving firstly under the influence of
Earth's magnetic field.
•
M
me pnltanceonotfincuoeils. untill the magnetic field of earth is parallel
wiothveth
•
•
•
Then, on application of an uknown current, a second magnetic field
on the axis of the coil which is perpendicular to the Earth's magnetic
field is created.
Hence the compass needle responds to the vector sum of the two
fields.
This deflection angle is equal to the tangent of the ratio of those two
fields.
APPLICATIONS
1. T.G. can be used to measure the magnitude of the horizontal component
of the geomagnetic field.
2. The principle can be used to compare the galvanometer constants.
3. For calibration of secondary instruments.
11
APPARATUS AND MATERIALS REQUIRED
➢
➢
➢
➢
➢
➢
Tangent Galvanometer (TG),
Commutator (C),
Rheostat (R),
Battery (E),
Ammeter (A),
Key (K),
Plug Key
12
Bo8tery%imin@or
Rheostot
13
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 8 with the direction H such that,
Eq 1: F = H tan 8
i!sieed1r
When a bar magnet is suspended in two Magnetic fields B and Bh,
it comes to rest making an angle 8 with the direction of Bh.
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,
0 2aIN
4a R
Let H is the horizontal component of earth's
14
magnetic field and the magnetic needle comes to rest at angle θ with the
direction of H, then according Eq. (1),
=
= 10−7 2πIN
Eq 3 :
= 2π×10−7IN
by substituting the value of current I, from eq. (3),
Eq 4:
= 0 2
4
RH
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 T.G coil relative to the earth’s
magnetic field H.
15
CIRCUIT DIAGRAM
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.
5. In this setting, 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).
16
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 tan8. 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 AND CALCULATIONS
Table 1. For variation of B with I
S.NO
Value of deflection 8 (degree) Mean
For direct
current
tan 8
Ammeter Reading (A)
For reverse
current
1.
'k5
d5
)'5
)'5
35
0.70
(if)
“Ud.âb‘*'
2.
3.
4.
5.
49
36
50
45
47
36
50
45
60
55
65
64
64
58
68
65
53.6
46.25
58.2
53.8
1.36
1.04
1.61
1.37
0.20
0.25
0.30
0.27
0.20
0.25
0.30
0.27
17
Table 2. For radius of tangent Galvanometer
S.No.
Inner
diameter
d1 (cm)
Outer
diameter d2
(cm)
Mean
diamete r
d
Mean
radius
(cm)
1.
16.0 × 10−2
16.40 × 10−2
16.20 × 10−2
8.10 × 10-2
2.
16.16 × 10−2
16.08 × 10−2
16.12 × 10−2
8.06 × 10−2
3.
16.06 × 10−2
16.10 × 10−2
16.08 × 10−2
8.04 × 10−2
Mean radius of coil R = 8.04 × 10−2
GRAPH
18
Slope of straight line = BC
AC
m = tan8
I
ows0$stJ$ute the m in Eq. (4),
4n RH
Then, H = = 7.6867 x 10 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 30° and 60°.
SOURCES OF ERROR
1. There may a magnetic material around apparatus.
2. The plane of coil will not be exactly in the magnetic meridian.
19
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.
20
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_Measurements/
Tangent_Galvanometer/Tangent_Galvanometer.html
➢ Galvanometer: Wikipedia, the free
encyclopediaen.wikipedia.org/wiki/Galvanometer