Two vessels of different materials are similar in size in every respect. The same quantity of ice filled in them gets melted in $20$ minutes and $40$ minutes respectively. The ratio of thermal conductivities of the materials is
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Hot water cools from ${60^o}C$ to ${50^o}C$ in the first $10$ minutes and to ${42^o}C$ in the next $10$ minutes. The temperature of the surrounding is ......... $^oC$
The area of a hole of heat furnace is ${10^{ - 4}}{m^2}$. It radiates $1.58 \times {10^5}$ calories of heat per hour. If the emissivity of the furnace is $0.80$ , then its temperature is....... $K$
A slab consists of two parallel layers of two different materials of same thickness having thermal conductivities $K_1$ and $K_2$ . The equivalent conductivity of the combination is
Two bodies $A$ and $B$ of same mass, area and surface finish with specific heats $S_A$ and $S_B\left(S_A > S_B\right)$ are allowed to cool for given temperature range. Temperature varies with time as ..........
If between wavelength $\lambda $and $\lambda + d\lambda $, ${e_\lambda }$and ${a_\lambda }$ be the emissive and absorptive powers of a body and ${E_\lambda }$ be the emissive power of a perfectly black body, then according to Kirchoff's law, which is true
Two rods of same length and cross section are joined along the length. Thermal conductivities of first and second rod are ${K_1}\,\,{\rm{and}}\,\,{K_2}$. The temperature of the free ends of the first and second rods are maintained at ${\theta _1}\,\,{\rm{and }}{\theta _2}$ respectively. The temperature of the common junction is
A black body at $227^o C$ radiates heat at the rate of $7\; cals/cm^2 s$. At a temperature of $727^o C$, the rate of heat radiated in the same units will be
If the initial temperatures of metallic sphere and disc, of the same mass, radius and nature are equal, then the ratio of their rate of cooling in same environment will be
A cup of tea cools from ${80^0}C$ to ${60^o}C$ in one minute. The ambient temperature is ${30^o}C$. In cooling from ${60^o}C$ to ${50^o}C$ it will take ....... $\sec$