physics questions???

Question

1)when the bulb of mercury in glass thermometere is inserted in boiling water the mercury column 1st droop slightly before it begins slightly before it begins to rise.account for this phenomeon..(consider wht happen intialy to the glass)

2)to help lower the high temprature of a sick patient an alcohol rub is sometime used. isopropyl alcohol is rubbed over the patient's back ,arms, legs etc. and allowed to evaporate. why does the work produce?

Answer 1

1) The glass expands, making the inner channel slightly larger. Since the heat yes yet to effect the mercury, it falls slightly to occupy the same volume as before, but in a larger cavity.

2) The evaporation causes cooling because the evaporation of liquids is an endothermic process. Energy is absorbed by the alcohol molecules in order to allow them to change state from a liquid into a gas.

Answer 2

Both answers for both questions are correct. But regarding cooling due to alcohol, there may be a counter question why does alcohol not take heat from surroundings to evaporate? To this I would say that , in evaporation molecules of alcohol which move faster enough to escape the surface tension do get out of alcohol. Thus preferably faster molecules leave alcohol than the slower ones. This in effect lowers the temperature of alcohol which then cools the body. In other words alcohol takes energy from itself to cool! That is why this energy is called internal energy(Latent heat).

Answer 3

1. the heat first causes the glass expand slightly, increasing its volume, causing the mercury to drop in height, but once heat it transferred to the mercury, it expands and rises up the column

2. alcohol absorbs energy from the body to evaporate into vapor, cooling the patient

Answer 4

Do you already know the answers?
Well, the first one the glass slightly expands when exposed to the hot temperature,

To your second question, the alcohol uses heat from the body to evapourate, lowering the temperature