Name: The Most Important Instrument
Uploaded: 2019-07-19
Duration: 7 min 34 s
Description: The more modern thermometer was invented in 1709 by Daniel Fahrenheit. In this video, we will learn about thermometers and how it is invented and used.

Question

A thermos is used to keep a hot liquid hot for a longer time. Do you think that a thermos flask can also keep cold water cool for a longer time?

Accepted Answer

Yes, a thermos flask can keep cold water cool for a longer time. The wall of a thermos flask is made up of two layers that do not touch each other. There is an area of vacuum between the two walls. Heat is not conducted across the vacuum and is hence preserved. Thus, the hot liquid inside the flask stays hot for a much longer time. Similarly, If we keep the cold liquid inside the thermos the same way due to the vacuum between the walls the coldness will remain the same for a longer time. A thermos flask maintains the temperature of the substance present in it. It keeps hot things hot and cold things cold for a long time. This is achieved by minimising the exchange of heat by conduction, convection and radiation. The vacuum between the glass walls prevents heat transfer by conduction. The tight stopper prevents air from entering or leaving the flask, so convection is not possible either. The silvered outer surface of the inner wall reduces heat exchange due to radiation.

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