HORIZONTAL COMPONENT OF EARTH’S
MAGNETIC FIELD USING TANGENT GALVANOMETER
To
determine the horizontal component of the Earth’s magnetic field using tangent
galvanometer.
Tangent
galvanometer (TG), commutator, battery, rheostat, ammeter, key and connecting
wires.
where,
BH
→ Horizontal component of the Earth’s magnetic field (T)
µ0
→ Permeability of free space (4π × 10−7 H m−1)
n
→ Number of turns of TG in the circuit (No unit)
k
→ Reduction factor of TG (A)
r
→ Radius of the coil (m)
·
The preliminary adjustments are carried
out as follows.
a.
The leveling screws at the base of TG are adjusted so that the circular turn
table is horizontal and the plane of the circular coil is vertical.
b.
The circular coil is rotated so that its plane is in the magnetic meridian
i.e., along the north-south direction.
c.
The compass box alone is rotated till the aluminium pointer reads 0° − 0°.
·
The connections are made as shown in
Figure (c).
·
The number of turns n is selected and
the circuit is switched on.
·
The range of current through TG is
chosen in such a way that the deflection of the aluminium pointer lies between
30° − 60°.
·
A suitable current is allowed to pass
through the circuit, the deflections θ1 and θ2 are noted from two ends of the
aluminium pointer.
·
Now the direction of current is reversed
using commutator C, the deflections θ3 and θ4 in the opposite direction are
noted.
·
The mean value θ of θ1, θ2,
θ3 and θ4 is calculated and tabulated.
·
The reduction factor k is calculated for
each case and it is found that k is a constant.
·
The experiment is repeated for various
values of current and the readings are noted and tabulated.
·
The radius of the circular coil is found
by measuring the circumference of the coil using a thread around the coil.
·
From the values of r, n and k, the
horizontal component of Earth’s magnetic field is determined.
It
is a kind of switch employed in electrical circuits, electric motors and
electric generators. It is used to reverse the direction of current in the
circuit.
Number
of turns of the coil n =
Circumference
of the coil (2Ï€r) =
Radius of the coil r =
The
horizontal component of Earth’s magnetic field is found to be ________
i)
The magnetic materials and magnets present in the vicinity of TG should be
removed.
ii)
The readings from the ends of the aluminium pointer should be taken without
parallax error.
iii)
The deflections of TG is restricted between 30° and 60°. It is because, the TG
is most sensi tive for deflection around 45° and is least sensitive around 0°
and 90°. We know that
I
= k tan θ
or
dI =k sec2 θ dθ
dθ/
dI = sin2θ / 2I
For
given current, sensitivity dθ / dI maximum for sin 2θ = 1 or θ = 45°
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