Question:medium

The pointer in a current measuring instrument returns to zero position when it is disconnected. This is due to ____.

Show Hint

Think of it like a spring-loaded door. The "deflecting torque" is you pushing the door open, while the "controlling torque" is the spring that pulls the door shut once you let go.
Updated On: Jul 14, 2026
  • mass of the moving part
  • balancing weight
  • controlling torque
  • damping torque
Show Solution

The Correct Option is C

Solution and Explanation

Picture the hairspring in a mechanical watch or the spiral spring in an old-style ammeter: as the pointer deflects, the spring winds up and stores energy, always pulling back toward its relaxed, zero position.

The mass of the moving parts is like the weight of the watch hands, it affects how easily the parts start or stop moving, but it has no built-in preference for where they end up.

A balancing weight is more like a counterweight that keeps the assembly level, it stops gravity from distorting the reading, but it does not pull the pointer anywhere in particular.

Damping is like a shock absorber, it smooths out the swing so the pointer does not overshoot or jitter, but a shock absorber alone, with no spring, would never bring anything back to a specific position.

It is the spring-like controlling torque that behaves exactly like the hairspring, always pulling the pointer back toward zero the moment the deflecting current is removed: \[ \boxed{\text{Controlling torque}} \]
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