उच्च परिवेश के तापमान के कारण एक स्थायी चुंबक चल कुंडली (PMMC) उपकरण में त्रुटियां होती हैं। इसका प्राथमिक कारण क्या है?

Which minimum set of instruments is required to measure the power factor of a balanced three-phase load?

Consider the following statements regarding the electrodynamometer-type instrument: i) It operates on the principle of a DC motor. ii) When used as a wattmeter, the instrument will have a non-uniform scale. iii) It is more expensive compared to a moving-iron instrument. iv) When the instrument is used in an AC circuit, there is no hysteresis loss in its operating torque mechanism. Which of the above statements are correct?