When a cold alcohol thermometer is placed in a hot liquid, the column of alcohol goes down slightly before going up. Explain why.
When a cold alcohol thermometer is placed in a hot liquid, heat is transferred from the liquid to the thermometer by thermal equilibrium.
However, during this transfer, the glass of the thermometer first get in touch with the liquid and thus it receives the heat and expands. In this turn, increase the inner volume of the thermometer but as the amount of content in the glass tube is constant; its level drops down a bit which can be noted by seeing the inscribed scale on the outer wall of the thermometer.
Now, the heat is transferred from the glass to the content of the thermometer and it then expands by getting this heat. Therefore, its level rises up. Thus, when a cold alcohol thermometer is placed in a hot liquid, the content level first goes down slightly then rises up.