Correct option is B
In a moving coil instrument, such as a moving coil galvanometer or an analog voltmeter/ammeter, an electro-dynamic type of instrument is used for both controlling and damping purposes. The moving coil instruments operate based on the interaction between the magnetic field produced by the current in the coil and the permanent magnetic field in the instrument.
Explanation of the Options:
(a) Electrostatic
Electrostatic instruments use electrostatic forces for measurement and are typically used for measuring high voltages.
They do not use moving coils for controlling and damping.
(b) Electro-dynamic
This is correct.
Electro-dynamic instruments use a moving coil placed in a magnetic field, where the interaction between the current in the coil and the magnetic field provides the controlling torque.
Damping is often achieved through eddy currents induced in a metal former attached to the coil.
(c) Moving iron
Moving iron instruments use a piece of iron that moves in response to magnetic fields generated by the current.
They are not used in moving coil instruments for controlling and damping.
(d) Thermocouple
Thermocouple instruments measure temperature by converting thermal energy into electrical energy and are not related to moving coil instruments for controlling and damping.
Therefore, the correct answer is (b) Electro-dynamic.
