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.
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 (2πr) =
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°