why does a potencial coil in wattmetter influences the pointer rotation
Can you try to explain me this




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When there is no power taken by the load, the pointer will be vertical - small springs in the mechanism work to provide a "zeroing" mechanical force.

As real power is consumed by the load the two current coils provide a north south magnetic field that the voltage coil attempts to align with. More current or more voltage means the alignment is better and, depending on flow of power, the needle points more to the left full-scale or more to the righ full-scale.

For AC it works the same except you must consider the phase angle between voltage and current. Should the phase angle between voltage and current be +/- 90 degrees there is no average net force produced by the alternating magnetic fields in the coils and the needle remains vertical.