Wattmeter is an instrument used to measure electric power. The most commonly used type of wattmeter is called an electrodynamic wattmeter. The electrodynamic wattmeter has two coils of wire. A fixed coil is arranged to receive the current of the circuit to be measured. A movable coil, supported by jeweled pivots that permit it to turn, is arranged to receive a current proportional to the voltage of the circuit to be measured. When the circuit is energized, the magnetic fields produced by the currents make the movable coil try to turn so that its axis is parallel to the axis of the fixed coil. Springs stop it in a position that depends on the power in the circuit. A pointer shows the power in watts on a scale.
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