What type of direct reading thermometer works on the principle of differential expansion of dissimilar metals as the temperature rises and features a rotary dial scale?

Correct Answer: Option A — Bimetallic thermometer

Bimetallic thermometers utilize a helical coil made of two dissimilar metals bonded together. Because each metal has a different coefficient of thermal expansion, the coil twists as temperature changes, mechanically driving the pointer on the dial. This provides a robust, direct-reading method for monitoring machinery temperatures.