down to ° F in minutes, what is the average rate of extra evaporation caused, by the drug. Assume the evaporation mechanism to be the only way by which heat is lost. The mass of the child is kg. The specific heat of human body is approximately the same as that of water, and latent heat of evaporation of water at that temperature is about cal g – .
. A ‘thermacole’ icebox is a cheap and an efficient method for storing small quantities of cooked food in summer in particular. A cubical icebox of side cm has a thickness of . cm.
If . kg of ice is put in the box, estimate the amount of ice remaining after h. The outside temperature is ° C, and co-efficient of thermal conductivity of thermacole is . J s – m – K – .
[Heat of fusion of water = × J kg – ] . A brass boiler has a base area of . m and thickness . cm.
It boils water at the rate of . kg/min when placed on a gas stove. Estimate the temperature of the part of the flame in contact with the boiler. Thermal conductivity of brass = J s – m – K – ; Heat of vaporisation of water = × J kg – .
. Explain why : (a) a body with large reflectivity is a poor emitter (b) a brass tumbler feels much colder than a wooden tray on a chilly day (c) an optical pyrometer (for measuring high temperatures) calibrated for an ideal black body radiation gives too low a value for the temperature of a red hot iron piece in the open, but gives a correct value for the temperature when the same piece is in the furnace (d) the earth without its atmosphere would be inhospitably cold (e) heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water . A