"Stephen Davenport" wrote in message
...
On Thursday, August 6, 2015 at 10:52:09 AM UTC-4, 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 ..."

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

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

==========

It does not and cannot, in the sense that I think you are representing it.
But you need to define what you mean by "cold" (see RedAcer's reply). Ypu
seem just to be citing relative temperatures.

In your example of the incubator, the hypothetical baby is not cooled by
cold "radiating" from the incubator wall. Instead, in a properly working
incubator the baby is radiating energy and steadily emitting warmth which is
radiated back equally by the incubator and the air therein.

All objects above absolute zero emit energy. But the baby may cool if an
incubator wall is colder than it should be, not because the wall is
"radiating cold" but because it is radiating less energy back to the baby
than the baby is emitting. There is net radiation from the baby to its
surroundings, and thus it cools (absent any biological processes). "A
premature baby in an incubator can be cooled dangerously by radiation...":
yes, by radiation *from* the baby (being greater than that towards it) is
what this means - not "cold radiation" in the other direction.

And of course a thermometer will measure a lower temperature adjacent to an
object that is emitting less radiation.

Stephen


Yes, Stephen is correct. All objects above absolute zero are emitting
radiation. A thermometer in a medium at constant temperature will only read
a constant value if the amount of radiation it is emitting is exactly
balanced by that it is receiving from its surroundings, e.g. it is in
radiative equilibrium. The amount of radiation emitted by the surroundings
will depend on their temperature. If a portion of the surroundings at a
given temperature is replaced by one at a lower temperature, the amount of
radiation received by the thermometer will fall, and the indicated
temperature of the thermometer will fall until the radiation emitted by the
thermometer matches the new value coming from its surroundings, and it
regains radiative equilibrium.

--
Bernard Burton

Wokingham Berkshire.

Weather data and satellite images at:
http://www.woksat.info/wwp.html



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