Which instrument shows the maximum “dip” effect (initial indication in the reverse direction during a rapid temperature change)?

Introduction / Context:
The “dip” effect refers to a temporary indication in the direction opposite to the true change during a rapid temperature step. This is caused by differing thermal time constants of an instrument’s components. Understanding which instruments are prone to such behavior helps technicians interpret readings during fast transients.

Given Data / Assumptions:

• We compare common temperature instruments: liquid-in-glass (mercury), bimetallic, thermocouple, and radiation pyrometer.
• The scenario is a sudden temperature rise (or fall), such as plunging a thermometer into a hot bath.
• “Dip” means an initial reverse movement before the correct trend dominates.

Concept / Approach:
In a mercury-in-glass thermometer subjected to a sudden temperature increase, the glass bulb heats and expands before the mercury column fully warms. The bulb’s expansion temporarily increases the bulb volume and lowers the mercury column height, producing an initial downward movement (a “dip”) even though the actual temperature is rising. As the mercury heats and expands more than the glass, the column rises and reaches the correct reading. This geometric-thermal interplay produces a pronounced dip compared with other instruments.

Step-by-Step Solution:

Verification / Alternative check:
Classic laboratory demonstrations show the mercury level dipping momentarily when a room-temperature thermometer is inserted into hot water, then recovering and rising to the new equilibrium reading.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing normal overshoot with the specific reverse dip mechanism caused by differential thermal expansion of glass vs. mercury.

Final Answer:
mercury-in-glass thermometer