Tell us about how the rotation of the frame with current is used in electrical measuring instruments

By the angle of rotation of the frame, you can determine the current strength in the conductor.
This fact is used in ammeters, voltmeters, etc.
When an electric current passes through the coil, a magnetic field is generated, which is amplified by an iron core. An ampere force acts on the coil and core, which moves the core coil out of the horizontal position, which deflects the arrow.

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