One liter of water at 30°C is mixed with one liter of water at 50°C. The temperature of the mixture will be:
$(a)$. 80°C
$(b)$. more than 50°C but less than 80°C
$(c)$. 20°C
$(d)$. between 30°C and 50°C

The correct answer is option $(D)$.

Explanation:

When a liter of water at 30°C is mixed with a liter of water at 50°C, there is a transfer of heat between the two liquids. Let us try to understand how heat is transferred between two liquids of different temperatures.

Heat transfer occurs from hot to cold objects

1. When two objects of different temperatures are brought in contact then heat is get transferred from the hot to cold objects. Therefore, after adding both liquids, the transfer of heat takes place from a liquid with a high temperature to a liquid with a low temperature. 
   
2. The heat never transfers from cold objects to hot objects.
   
3. There is no heat transfer between two objects of the same temperature.

Conclusion:

When a liter of water at 30°C is mixed with a liter of water at 50°C, there is a transfer of heat between the two liquids. The temperature of the mixture will be more than $30^{\circ}\ C$ and less than $50^{\circ}\ C$. The temperature of the mixture will be between $30^{\circ}\ C$ and $50^{\circ}\ C$ because the volume of both the liquids with a temperature of $30^{\circ}\ C$ and $50^{\circ}\ C$ is equal. Therefore, after adding both liquids, the transfer of heat takes place from a liquid with a high temperature to a liquid with a low temperature. That's why the temperature remains between $30^{\circ}\ C$ and $50^{\circ}\ C$.

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Updated on: 10-Oct-2022

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