Why moving iron instruments work on AC and DC supply both but moving coil instruments work only in DC supply only ? 
What is difference between moving coil and moving iron ammeter?
Why is the core of a moving coil galvanometer taken as a soft iron cylinder? What is current sensitivity of a moving coil galvanometer? The core of a moving coil galvanometer is made of soft iron, why? What is the difference between an ammeter and a voltmeter? How hot does moving metal need to be to generate an electromagnetic field? What is the basic difference between inductor and coil? Why does a current carrying coil produce magnetic field? How is flux produced in a coil? What is the reason for the presence of a single coil and inductor coil in the wattmeter? An electric iron has a rating of 750W , 220V. Calculate the current passing through it and its resistance when in use? How does a coil in a magnetic field rotate through a full turn? Differentiate primary coil from the secondary coil of a transformer? Can we increase/decrease range of an ammeter? Why is an ammeter always connected in series and a voltmeter always in parallel in a circuit? How can the range of an ammeter be extended? What is the difference between electrode, filler metal and welding rod? How does a current-carrying conductor produce a magnetic field when made into a coil? If magnetic fields can't do work, how can one magnet physically move another? What is the difference between magnetic flux and magnetic flux linkage? In a magnetic crane, a powerful electromagnet is used to lift up the iron material. But when we pass a current through a conductor & bring iron filings near it, they are set in a concentric manner, instead of clinging the conductor. Why? How does an electronic and a wire transfer differ? In a magnetic crane, a powerful electromagnet is used to lift up the iron material. But when we pass a current through a conductor & bring iron filings near it, they are set in a form of concentric circles, instead of clinging to the conductor. Why? Theory of 3 ammeter method? Why electric coil draws overcurrent? What is the use of tesla coil? What is a magnetometer sensor? How does a metal detector work? A longer iron bar and a shorter iron bar are exposed to the same magnetic field.Would the total magnetic flux produced in them be the same? What is the difference between magnetic flux and magnetic field? What is the difference between heat transfer and work transfer? What is the difference between a wind vane and a anemometer? What are some examples?