Question

explain why electrodynamic instrument can be uses both on AC and DC??​

Answer 1

Answer:

There are two basic types of dynamometer

attraction type

repulsion type..

These moving iron instruments work on following priciple..

The current in the circuit is taken to a coil,which behaves as electromagnet and this magnetises the soft iron core placed nearby,which has the pointer attached and subsequently give readings.

What happens is if we have D.C to measure,magnetic poles created shall not alter,due to unidirectional current,and the magnetised material is attracted or repeled(depends on type of dynamometer). This force of interaction acts as Deflecting torque,and spring or weight balance can be used as controlling torque..

For A.C,they still work as in repulsion type meters,there are two magnetic bars one is fixed amd other one moves under force of repulsion due to former..pointer is attached to later.

Now if current changes polarity(definition of ac),the magnetic poles also interchange..

But the changing effect is similar in both the bars,why??

Because if North-North pole repelled earlier,and due to change in current,we have south-south at the ends of iron bars..But,it doesn't matter as south-south repels again and our instrument works just fine…