On 06/08/2015 15:52, Alastair wrote:
Dawlish,

On Page 576 of University Physics with Modern Physics, Technology Update, Thirteenth Edition (2010), which continues
to set the benchmark for clarity and rigor combined with effective
teaching and research-based innovation, they write:

"Radiation. Heat transfer by radiation is important in some surprising places.
A premature baby in an incubator can be cooled dangerously by
radiation if the walls
of the incubator happened to be cold, even when the air in the
incubator is warm.
Some incubators regulate the temperature measuring the baby's skin ..."

This doesn't sound at all right.

Convection dominates radiation transfer at temperatures below about 53C
under NTP ambient laboratory conditions - the baby is cooled by a pool
of cold air due to a cold draft coming off the cool glass walls.

Hot objects radiate heat which warms adjacent objects. Cold objects radiate cold which cools adjects objects.

This is complete and utter clueless dross. I hope that it is you who
have misunderstood what the textbook actually says, but I have a bad
feeling this may well indicate the dumbing down of the hard sciences.

*Everything* radiates thermal energy according to Plank's law usually
approximating a black body according to its temperature.

https://en.wikipedia.org/wiki/Black-body_radiation
https://en.wikipedia.org/wiki/Stefan...3Boltzmann_law

Energy *transfer* between bodies varies according to the difference
between the fourth power of their absolute temperatures. Net energy flow
always being from the hotter to the cooler body.

The Earth's temperature ~290K is determined by being in thermal
equilibrium with one sun at 5500K subtending an angle of 0.01 radians
and ~4pi of empty space radiating at 4K (the microwave background).

Earth gains energy from the sun and thermalises it and loses energy to
the sky but nowhere is there any "cold radiation" it is an idiotic
phrase worthy only of charlatans and fools.

Everything radiates thermal radiation to everything else in an amount
determined by its absolute temperature and surface emissivity.

The latter is difficult to demonstrate because it is more difficult to maintain a constant cold temperature than a high temperture.
The latter is easy using electrical heating. However, holding a
thermnometer over an object taken from a freezer will cause the
temperature shown to drop.

Yes. Because the cold object below the thermometer is no longer
radiating at the same temperature as the rest of the surroundings. It is
the thermometer that is on average donating heat radiation to the cold
block which is not being returned any more in sufficient amount to
maintain its temperature. It is not evidence of "cold radiation" the
term is a complete misnomer and dangerously misleading.

I hope you will now realise that you are wrong, will apologise and admit your mistake. Cold radiation does exist.

Cheers, Alastair.

Sorry no it doesn't. If that "physics" book really does say what you
claim then it has no right to be sold as a university textbook!

I don't often defend Dawlish but on this point he is absolutely correct.

--
Regards,
Martin Brown