Physics Questions and Answers – Thermal Properties of Matter – Newton’s Law of Cooling

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Thermal Properties of Matter – Newton’s Law of Cooling”.

1. The rate of cooling of water increases with fall in temperature. True or False?
a) True
b) False
View Answer

Answer: b
Explanation: The graph of temperature difference with time given below shows that as temperature decreases rate of cooling (or temperature difference per unit time) also decreases. We can see that for the same time interval temperature difference becomes less at lower temperatures.

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2. A body has a temperature of 200°C and is kept in a room containing air at 25°C. We can use Newton’s law of cooling. True or False?
a) True
b) False
View Answer

Answer: b
Explanation: Newton’s law of cooling can only be used when the temperature difference is small which is not the case in the given scenario. So, the given statement is false.

3. A liquid cools from 65°C to 55°C in 5 mins. If the surrounding temperature is 35℃, calculate the time taken for temperature to fall from 45°C to 35°C.
a) 25sec
b) 25min
c) 30min
d) 30sec
View Answer

Answer: b
Explanation: Average temperature of liquid in the first case = 60℃.
Rate of fall of temperature = 65-55 / 5 = 2°C /min.
Which is also equal to k(60 – 35) = 25k, where k is a constant.
∴ 25k = 2 Or k = 2/25
Average temperature in the second case = 40°C
Rate of fall of temp = 45 – 35 / t = k(40-35)
∴ t = 25mins.
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