Transmission Of Heat Question 105
Question: The only possibility of heat flow in a thermos flask is through its cork which is 75 cm2 in area and 5 cm thick. Its thermal conductivity is 0.0075 cal/cmsecoC. The outside temperature is 40oC and latent heat of ice is 80 cal g?1. Time taken by 500 g of ice at 0oC in the flask to melt into water at 0oC is
[CPMT 1974, 78; MNR 1983]
Options:
A) 2.47 hr
B) 4.27 hr
C) 7.42 hr
D) 4.72 hr
Show Answer
Answer:
Correct Answer: A
Solution:
$ mL=\frac{KA\Delta \theta ,,t}{\Delta x} $
Therefore $ 500\times 80=\frac{0.0075\times 75\times (40-0)t}{5} $
Therefore t = 8.9 ´ 103 sec = 2.47 hr.
BETA
