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Examoogle • User • info@examoogle.com • EE-2024-8821
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The deflecting torque in an instrument may be produced
Magnetically
Electrostatically
Thermally
Any of the above
Any of the above
Quick Summary: An electrical measuring instrument produces a deflecting torque ($T_d$) using various physical effects to move the pointer from its zero position. Since different physical phenomena—magnetic, electrostatic, thermal, or electrodynamic—can result in mechanical force, the torque can be produced by any of these methods depending on the instrument's design.
An electrical measuring instrument produces a deflecting torque (Td) using various physical effects to move the pointer from its zero position. Since different physical phenomena—magnetic, electrostatic, thermal, or electrodynamic—can result in mechanical force, the torque can be produced by any of these methods depending on the instrument's design.
Td=NBIAcosθ — Deflecting torque for moving coil instruments
Td=21V2dθdC — Deflecting torque for electrostatic instruments
Deflecting torque is essential to overcome inertia and friction.
Magnetic deflection is used in PMMC and Moving Iron meters.
Electrostatic deflection is primarily used for high-voltage voltmeters.
Thermal effect (heating) is used in hot-wire or thermocouple instruments.
Flexibility in instrument design based on the measured parameter (voltage vs current).
Allows for diverse operating environments (AC/DC capability).
Thermal instruments have slow response times.
Electrostatic instruments are sensitive to stray capacitance.
PMMC instruments (Magnetic)
Voltmeters (Electrostatic)
Thermocouple RF ammeters (Thermal)
All three methods provide a mechanical force that moves the pointer across a calibrated scale.
The choice of method depends on the sensitivity, range, and type of signal (AC/DC) being measured.
D is correct — The deflecting torque can be generated using various physical phenomena including magnetic, electrostatic, and thermal effects depending on the construction of the measuring instrument.
Always remember that every analog instrument requires three torques: Deflecting (to move), Controlling (to balance), and Damping (to stop oscillation).