Chapter - 15
Q.1: What is the function of the concave pole pieces and the coaxial soft iron cylinder in the moving coil galvanometer?
Ans: The concave magnetic poles and the cylindrical core make the magnetic field radial and stronger (so the current becomes directly proportional to the deflection).
Q.2: Why is it necessary to have some form of controlling couple in the moving coil galvanometer?
Ans: Controlling couple is necessary to control the motion of the coil, it is proportional to the current to be measured. It is produced by using a spring control method, which consists of two hair springs attached to a spindle wound in the opposite directions. As the coil rotates the spring winds up and produces a counter torque. The coil comes to rest (the final deflection of the pointer is given) when the deflecting torque (or magnetic torque) is counterbalanced by the controlling torque (or restoring torque).
