Question

Q1) Choose the right answer from the following questions: 1) A pointer of an instrument once deflected returns to zero position, when the current is removed due a) Action of gravity b) Mass of the pointer c) Controlling Torque d) Damping Torques

Answer 1

There are three torques for any electromagnetic Devices Deflecting Torque, Controlling Torque, and Damping Torque.

Deflecting Torque :- When we apply voltage or current to the device it will generate torque proportional to the value of voltage or current and will move the pointer, which will indicate the value on the scale.

But there is one problem if we only apply Deflecting Torque on the pointer it will not stop at any point. We need some kind of torque in reverse direction which will stop the pointer at right position this torque is called controlling torque and it's normally provided with spring or some weight ( gravity control ) which can provide torque in the other direction.

When Deflecting and controlling torque are equal it will cancel out each other and will show correct value on the scale.

Other use of controlling torque is to move pointer to its initial position, without this it would stay at measured value.( Our Answer )

Damping Torque :- work of this torque is to damp the system which means minimize the oscillation of the pointer at the measured value. Can be provided with air friction, liquid friction or eddy current effect.

Option one can be ture if we would use gravity control method for our device but there is more clear option of CONTROLLING TORQUE.