MCQ Detailed View

The measurement of temperature is a fundamental task in physics and chemistry, and the choice of thermometer depends on the temperature range being studied. The boiling point of water under normal atmospheric pressure is 100°C (373 K). To measure this temperature accurately, a thermometer must be able to withstand high temperatures without evaporating or losing accuracy.

A mercury thermometer is the most suitable instrument for measuring the boiling point of water. Mercury, a liquid metal, has several properties that make it ideal:

1. 
   

   Wide Temperature Range – Mercury thermometers can measure from about −39°C up to 356°C, which easily covers the boiling point of water.

   
   


2. 
   

   Thermal Stability – Mercury does not vaporize or expand excessively at 100°C, so it provides reliable and repeatable readings.

   
   


3. 
   

   Non-adhesive Property – Mercury does not stick to the walls of the thermometer tube, ensuring a clear meniscus for accurate measurement.

   
   


4. 
   

   Precision – The expansion of mercury is uniform, making the thermometer highly accurate compared to other liquid thermometers.

   
   

In contrast:

• 
  

  Alcohol thermometers are better for measuring very low temperatures, even below −100°C, but alcohol boils at around 78°C, making them unsuitable for measuring the boiling point of water.

  
  


• 
  

  Liquid crystal thermometers work only over a narrow temperature range (usually for body temperature or surface applications) and are not reliable for high temperatures.

  
  


• 
  

  Bimetallic thermometers are robust and used in industrial processes, but they are less precise compared to mercury thermometers for laboratory measurements.

  
  

Thus, when measuring the boiling point of water in laboratories, the mercury thermometer is preferred. It provides accuracy, reliability, and covers the required temperature range without risk of liquid evaporation.

In conclusion, while other thermometers have specialized uses, the mercury thermometer remains the most suitable for determining the boiling point of water, making it the correct choice in this Physics MCQ.