The correct answer is: C. dynamometer instrument
A Weston synchronoscope is a type of dynamometer instrument. It is used to measure the phase angle between two alternating current (AC) waveforms. The instrument consists of two coils, one fixed and one rotating. The fixed coil is connected to a reference voltage, and the rotating coil is connected to the voltage being measured. The current flowing through the two coils creates a magnetic field, which interacts to produce a torque on the rotating coil. The amount of torque is proportional to the phase difference between the two voltages. The instrument is calibrated to read the phase angle directly.
A moving coil instrument is a type of electrical instrument that uses a moving coil to measure current or voltage. The moving coil is suspended in a magnetic field, and the current or voltage to be measured creates a force on the coil. The coil is attached to a pointer, which moves across a scale to indicate the measurement.
A moving iron instrument is a type of electrical instrument that uses a moving iron to measure current or voltage. The moving iron is placed in a magnetic field, and the current or voltage to be measured creates a force on the iron. The iron is attached to a pointer, which moves across a scale to indicate the measurement.
None of the above is not a correct answer.