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Question
One day in the morning, Ramesh filled up 1/3 bucket of hot water from geyser, to take bath. Remaining 2/3 was to be filled by cold water (at room temperature) to bring mixture to a comfortable temperature. Suddenly Ramesh had to attend to something which would take some times, say 5-10 minutes before he could take bath. Now he had two options: (i) fill the remaining bucket completely by cold water and then attend to the work, (ii) first attend to the work and fill the remaining bucket just before taking bath. Which option do you think would have kept water warmer? Explain.
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Solution
Using the concept of Newton’s law of cooling, we can say that rate of cooling is directly proportional to the difference in the temperature of the body and surroundings.
According to the first option, the water should be warmer, as the difference between the temperature of the surroundings and the water is small, therefore, less heat is lost.
According to the second option, the heat lost is more, as the difference between the surroundings and water is large.
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