Transmission Of Heat Question 177
Question: A liquid cools down from $ 70^{o}C $ to $ 60^{o}C $ in 5 minutes. The time taken to cool it from $ 60^{o}C $ to $ 50^{o}C $ will be
[MP PET 1992, 2000; MP PMT 1996]
Options:
A) 5 minutes
B) Lesser than 5 minutes
C) Greater than 5 minutes
D) Lesser or greater than 5 minutes depending upon the density of the liquid
Show Answer
Answer:
Correct Answer: C
Solution:
According to Newton’s law of cooling Rate of cooling µ mean temperature difference. Initially, mean temperature difference $ =( \frac{70+60}{2}-{\theta _{0}} )=(65-{\theta _{0}}) $ Finally, mean temperature difference $ =( \frac{60+50}{2}-{\theta _{0}} )=(55-{\theta _{0}}) $ In second case mean temperature difference decreases, so rate of fall of temperature decreases, so it takes more time to cool through the same range.
BETA
