Question 26.73: A coil of current-carrying Nichrome wire is immersed in a li......
A coil of current-carrying Nichrome wire is immersed in a liquid. (Nichrome is a nickel-chromium-iron alloy commonly used in heating elements.) When the potential difference across the coil is 12 V and the current through the coil is 5.2 A, the liquid evaporates at the steady rate of 21 mg/s. Calculate the heat of vaporization of the liquid (see Section 18-8).
The rate at which heat is being supplied is P = iV = (5.2 A)(12 V) = 62.4 W. Considered on a one-second time-frame, this means 62.4 J of heat are absorbed by the liquid each second. Using Eq. 18-16, we find the heat of transformation to be
Q = Lm. (18-16)
L=\frac{Q}{m}=\frac{62.4 \mathrm{~J}}{21 \times 10^{-6} \mathrm{~kg}}=3.0 \times 10^6 \mathrm{~J} / \mathrm{kg} .