What is the principle on which moving iron instruments operate?

The principle that the iron plate is attracted towards a magnetic field, with the force of attraction depending on the strength of the magnetic field.

Fill in the blank: The moving iron instrument uses a ______ as an electromagnet.

Stationary coil

True or False: The deflection of moving iron instruments is directly proportional to the current flowing through the coil.

False. The deflection torque is proportional to the square of the current.

Riddle: I am an instrument that attracts an iron vane from lower to higher magnetic fields. What am I?

Attraction type moving iron instrument

Which type of moving iron instrument has two vanes that repel each other?

Repulsion type instrument

Fill in the blank: The main error in moving iron instruments due to the magnetic properties of iron is called ______.

Hysteresis error

What are the two types of errors present in moving iron instruments?

Errors occurring in both AC and DC, and errors occurring only in AC.

True or False: Electrodynamometer instruments can be calibrated with a DC source and used for AC measurements without modification.

True.

Riddle: I can read both AC and DC, with a scale that is not uniform due to my square-law response. What am I?

Electrodynamometer-type instrument

What is the main advantage of electrodynamometer-type instruments?

They can be used for accurate measurements of RMS values for both AC and DC.