Q: Why is greater time required to measure the temperature of a human body with the thermometer than to shake it down to the initial ambient temperature ?
Sol: The rate of heat transfer from a hot body to a cold one depends on conduction , convection and radiation – all of which depend on the temperature difference . Because of the small difference in temperature between thermometer and the temperature of human body and conduction being the only form of heat transfer , it takes longer to record the temperature of human body . When the warm thermometer is then brought into contact with the air in the room , the mercury column drops faster due to greater rate of heat loss . This is further accelerated when the thermometer is shaken .