MCQ Detailed View

Water is widely used as a coolant in car engines because it has a very high specific heat capacity, meaning it can absorb and store a large amount of heat energy before its temperature rises significantly. This property makes water ideal for transferring heat away from the engine and preventing overheating during operation.

The specific heat capacity of water is approximately 4.18 joules per gram per degree Celsius (J/g°C). This is much higher than that of most other common liquids. As a result:

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  Water can absorb large quantities of heat generated by engine combustion processes.

  
  


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  It maintains a stable temperature, preventing rapid overheating.

  
  


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  Heat is transferred efficiently from the engine to the radiator, where it is dissipated into the air.

  
  

While water is also a good conductor of heat and boils at a relatively high temperature, these properties are secondary compared to its capacity to store thermal energy. Evaporation of water can produce cooling, but in a car’s cooling system, water usually circulates in a closed system, so evaporation is minimal.

The other options are less accurate:

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  Good conductor of heat: Helps in heat transfer but does not explain water's ability to absorb large amounts of heat energy.

  
  


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  High boiling point: Water boils at 100°C under normal pressure, which is beneficial but not the main reason for its cooling efficiency.

  
  


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  Evaporation produces cooling: True in open environments (like sweating), but not the primary cooling process in engines.

  
  

Because of its high specific heat capacity, water can regulate engine temperature effectively, reducing the risk of overheating and preventing damage to engine components. This is why water (often mixed with antifreeze to prevent freezing and corrosion) is the most commonly used engine coolant worldwide.