Q. The two opposite faces of a cubical piece of iron (thermal conductivity $= 0.2\ CGS$ unit) are at $100℃$ and $0℃$ in ice. If the area of a surface is $4cm^{2}$, then the mass of ice melted in a 10 minutes will be
A) $30\ g$
B) $300\ g$
C) $5\ g$
D) $50\ g$
Explanation
(b) $Q = mL = KA\frac{(\theta_{1} - \theta_{2})}{l}t \Rightarrow m = \frac{1}{L} \times KA\frac{(\theta_{1} - \theta_{2})}{l} \times t$
$= \frac{1}{80} \times 0.2 \times 4 \times \frac{(100 - 0)}{\sqrt{4}} \times 10 \times 60\ \left\lbrack \because l^{2} = 4 \Rightarrow l = \sqrt{4}\ \right\rbrack$
$= \frac{0.2 \times 4 \times 100 \times 600}{80 \times 2} = 300\ gm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.