Which instrument is commonly associated with a variable resistor gauge?

• A. Ammeter.
• B. Barometer.
• C. Voltmeter.
• D. Ratiometer type instrument.

Answer: (D)

The idea being tested is how a reading is generated when a gauge uses a variable resistor as its primary sensing element. A variable resistor gauge relies on a resistor whose value changes with the quantity being measured, and the instrument’s movement is driven by detecting that change, typically through a bridge or ratio-detection arrangement. Ratiometer type instruments are designed around this principle, using a potentiometer-style network to compare signals and produce a reading proportional to their ratio. In contrast, the other instruments operate by different mechanisms—an ammeter uses current flowing through a shunt or coil, a barometer senses atmospheric pressure with a diaphragmatic element, and a voltmeter measures potential difference with its own movement or resistance setup—not a gauge driven primarily by a variable resistor. So, the instrument most closely associated with a variable resistor gauge is the ratiometer type instrument.