Which physical change causes the pointer of a dial thermometer to move when measuring temperature?

• A. Change in color of a liquid inside the thermometer
• B. Generation of an electric current by a thermocouple
• C. Evaporation of mercury from the thermometer bulb
• D. Expansion or contraction of a metal coil inside the thermometer

Answer: (D)

Verified step by step guidance

1. Understand that a dial thermometer measures temperature by converting thermal expansion or contraction into mechanical movement.
2. Recognize that when temperature changes, the metal coil inside the thermometer either expands or contracts due to thermal expansion properties of metals.
3. This expansion or contraction causes the coil to twist or untwist, which moves the pointer on the dial to indicate the temperature.
4. Note that changes in color of a liquid or evaporation of mercury are not responsible for moving the pointer in a dial thermometer; those relate to other types of thermometers.
5. Also, generation of electric current by a thermocouple is a different temperature measurement method and does not apply to dial thermometers.