Q. A substance of mass $m\ kg$ requires a power input of $P$ watts to remain in the molten state at its melting point. When the power is turned off, the sample completely solidifies in time $t$ sec. What is the latent heat of fusion of the substance
A) $\frac{Pm}{t}$
B) $\frac{Pt}{m}$
C) $\frac{m}{Pt}$
D) $\frac{t}{Pm}$
Explanation
(b) Heat lost in $t\sec = mL$ or heat lost per sec $= \frac{mL}{t}.$ This must be the heat supplied for keeping the substance in molten state per sec.
$\therefore\frac{mL}{t} = P\ or\ L = \frac{Pt}{m}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.