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Question
A glass full of hot milk is poured on the table. It begins to cool gradually. Which of the following is correct?
- The rate of cooling is constant till milk attains the temperature of the surrounding.
- The temperature of milk falls off exponentially with time.
- While cooling, there is a flow of heat from milk to the surrounding as well as from surrounding to the milk but the net flow of heat is from milk to the surounding and that is why it cools.
- All three phenomenon, conduction, convection and radiation are responsible for the loss of heat from milk to the surroundings.
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Solution
b, c and d
Explanation:
When hot milk spreads on the table heat is transferred to the surroundings by conduction, convection and radiation. Because the surface area of poured milk on a table is more than the surface area of milk filled in a glass. Hence, its temperature falls off exponentially according to Newton’s law of cooling. Heat also will be transferred from the surroundings to the milk but will be lesser than that transferred from milk to the surroundings.
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