CBSE Class 12-science Answered
Moving coil galvanometer
Principle: A current carrying coil suspended in a magnetic field experiences a torque.
Let I be the current through the loop PQRS.
a, b = Sides of the rectangular loop
A = ab = Area of the loop
N = Number of turns in the loop
According to Fleming's left hand rule, the side AB experiences a normal inward force, F1= IaB and side CD experiences a normal outward force, F2 = IaB. These two equal and opposite forces form a couple, which exerts a torque given by,
= Force × Perpendicular distance
= IaB × b sin
= IBab sin
τ = IBA sin
For N turns,
τ = NIBA sin
The current sensitivity of a moving coil galvanometer depends on
(i) number of turns in the galvanometer coil
(ii) torsional constant of the suspension fibre.
Or
Biot-Savart law states that the magnetic field dB due to the current element dl at any point P is
(i) directly proportional to the current I, dB I
(ii) directly proportional to the length dl of the element, dB dl
(iii) directly proportional to sin, where is the angle between dl and r, dBsin
(iv) inversely proportional to the square of the distance r from the current element AB,
From (i), (ii) , (iii), and (iv), we obtain
At centre, x = 0