Cold Radiation
On Monday, 26 September 2016 18:50:02 UTC+1, wrote:
On Monday, 26 September 2016 12:43:48 UTC+1, Alastair wrote:
Dawlish discussed the science for once and brought a point which I think is what is confusing everyone.
He wrote "'...heat *always* flows spontaneously from hotter to colder bodies, and *never* the reverse, unless external work is performed on the system'
https://en.wikipedia.org/wiki/Second_law_of_thermodynamics#Intuitive_meaning_of_ the_law"
But the sentence actually reads "FOR EXAMPLE, heat always flows spontaneously from hotter to colder bodies ...". That is not a statement of the second law, it is an example. Another example is that cold always flows from a colder to a hotter body unless external work is performed on the system e..g a refigerator.
Putting it another way hot objects always cool and cold objects always warm e.g, cup of coffeee and an ice cube. But hot cups of coffe are so common it is easy to forget about cold ice cubes. (Thanks Asha for reminding me.)
Moreover, as I have already explained, the difference in temperature between and ice cube and room temperature is much less than that between a boiling kettle and room temperature. It is only when you have a tray of ice cubes and you use the back of your hand that you can sense the cold radiation.
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