A bucket full of hot water is kept in a room and it cools from 80°C to 75°C in T1 minutes, from 75°C to 70°C in T2 minutes and from 70°C to 65°C in T3 minutes. Then

  1. T1 < T3 < T2
  2. T1 = T2 = T3
  3. T1 < T2 < T3
  4. T1 > T2 > T3

Answer (Detailed Solution Below)

Option 3 : T1 < T2 < T3
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Detailed Solution

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Concept:

Newton’s law of cooling

  • According to Newton’s law of cooling, the rate of loss of heat from a body is directly proportional to the difference in the temperature of the body, and its surroundings.
  • Mathematically it is given as,

Where 

  • Tt = temperature at time t
  • Ts = temperature of the surrounding
  • k = Positive constant that depends on the area and nature of the surface of the body under consideration
  • dt = time required

Explanation:

  • According to Newton’s law of cooling, the smaller the temperature difference between the body and the surroundings, the smaller is the rate of cooling, and the more is the time taken to cool. Or, in other words, the hotter the body, the faster it cools.

So,

⇒ T< T2 < T3

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