Define emissivity of the surface of body? What are its value for a completely reflecting and perfectly black body?

Thermal conductivity of copper $=385 \mathrm{W} {\mathrm{m}}^1{ }^{\circ }{\mathrm{C}}^{-1}$

The left end of a copper rod (length$= 20 \mathrm{cm}$, area of cross-section $= 0.20 {\mathrm{cm}}^2$) is maintained at ${20}^{\circ }\mathrm{C}$ and the right end is maintained at ${80}^{\circ }\mathrm{C}$. Neglecting any loss of heat through radiation,

(a) Find the temperature at a point $11 \mathrm{cm}$ from the left end and

(b) Find the heat current through the rod.

A cylindrical rod with one end in a steam chamber and the other end in ice results in melting of 0.1 gm of ice per second. If the rod is replaced by another rod with half the length and double the radius of the first and if the thermal conductivity of the material of the second rod is 0.25 times that of first, the rate at which ice melts in gm/second will be :

In the steady state of temperature at the end of a copper rod of length $25cm$ and area of cross-section $1.0c{m}^2 are {125}^{\circ }C and 0^{\circ }C$ respectively. Calculate the temperature gradient, rate of heat flow and the temperature at a distance $10cm$ from the hot end. $[K for copper =9.2\times {10}^{-3} kilocal/m{ }^{\circ }C-s]$

Latent heat of vaporization of water$=2\cdot 26\times {10}^6 Jk{g}^{-1}.$ when water is boiled in a container having a bottom of surface area $25c{m}^2$, thickness $1\cdot 0mm$ and thermal conductivity $50 W{m}^{-10}{C}^{-1}.$ $100g$ of water is converted into steam per minute in the steady state after the boiling starts. Assuming that no heat is lost to the atmosphere, calculate the temperature of the lower surface of the bottom. $$

The area of glass of a window of a room is $10 m^2$ and thickness is $2mm.$The outer and inner temperatures are $40°C$and $20°C$ respectively. Thermal conductivity of glass in S.I unit is$0.2.$ The heat flowing in the room per second will be :