Which of the following error in moving iron type instruments can be removed by connecting a capacitor of suitable value in parallel with the swamp resistance of the instrument?

Option 1 : Error with a.c. work only

Concept: Since swamping resistor and capacitor are used to reduce frequency-related error in MI instruments therefore for Errors involving AC source, the parallel combination of swamp resistor and capacitor is used.

Explanation: 

• In moving iron instruments, the change in frequency causes an error due to the change in magnitude of eddy currents set up in the metal portion of the instruments.
• The reactance of the operating coil changes by the change in frequency.
• At high frequencies, the meter will give a reading lower than the actual value and at low frequencies, the meter gives a reading higher than the actual.
• This type of error can be eliminated only if the impedance of the coil is independent of the frequency. This is achieved by having a capacitance in shunt with the swamping resistance of the coil as shown in the figure;