Q. An ice box made of Styrofoam (Thermal conductivity=0.01${Jm}^{- 1}s^{- 1}K^{- 1}$) is used to keep liquids cool. It has a total wall area including lid of 0.8${\ m}^{2}$ and wall thickness of 0.2 cm. A bottle of water is placed in the box and filled with ice. If the outside temperature is 30$℃$ the rate flow of heat into the box is (in ${Js}^{- 1}$)
A) 16
B) 14
C) 12
D) 10
Explanation
(c) Heat current, $H = \frac{\mathcal{Q}}{t} = \ \frac{KA(\theta_{1} - \theta_{2})}{d}$
= $\frac{0.01 \times 0.8(30{^\circ} - 0{^\circ})}{2 \times 10^{- 2}}$ = 12 J$s^{- 1}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.