skin temperature may be 28° ° C (say). The

skin temperature may be ° ° C (say). The emissivity of the skin is about . for the relevant region of electromagnetic radiation. The rate of heat loss is: H = . × – × . × . × {( ) – ( ) } = . W which is more than half the rate of energy production by the body at rest ( W). To prevent this heat loss effectively (better than ordinary clothing), modern arctic clothing has an additional thin shiny metallic layer next to the skin, which reflects the body’s radiation. . NEWTON’S LAW OF COOLING We all know that hot water or milk when left on a table begins to cool, gradually. Ultimately it attains the temperature of the surroundings. To study how slow or fast a given body can cool on exchanging heat with its surroundings, let us perform the following activity. Take some water, say mL, in a calorimeter with a stirrer and cover it with a two-holed lid. Fix the stirrer through one hole and fix a thermometer through another hole in the lid and make sure that the bulb of thermometer is immersed in the water. Note the reading of the thermometer. This reading T is the temperature of the surroundings. Heat the water kept in the calorimeter till it attains a temperature, say ° C above room temperature (i.e., temperature of the surroundings). Then, stop heating the water by removing the heat source. Start the stop-watch and note the reading of the thermometer after a fixed interval of time, say after every one minute of stirring gently with the stirrer. Continue to note the temperature ( T ) of water till it attains a temperature about ° C above that of the surroundings. Then, plot a graph by taking each value of temperature ∆ T = T – T along y-axis and the coresponding value of t along x-axis (Fig. . ). Fig. . Curve showing cooling of hot water with time. From the graph you can infer how the cooling of hot