On Saturday, 24 September 2016 16:09:26 UTC+1, Asha Santon wrote:
On 2015-08-06 14:52:07 +0000, Alastair said:

Cold radiation does exist.

Cheers, Alastair.

I am not arguing or taking sides (hard to believe, I know) but please
consider this.

Place an ice cube on a suitable surface (use tongs to protect your body
heat) and move your forefinger near to it until you feel the cooling
effect. This is caused by:

a) The cold is radiating from the ice cube, causing your fingertip to
feel less warm than before, or

b) The warmth from your finger is radiating towards the cooler ice
cube, causing your fingertip to feel less warm than before.

Then try this.

Put a kettle on to boil and move a fingertip towards the body of the
kettle until you feel the heat (taking great care not to burn
yourself). This is caused by:

c) The heat is radiating from the kettle, causing your fingertip to
feel warmer than before, or

d) The relative cold from your finger is radiating towards the kettle,
causing your fingertip to feel warmer than before.

The explanations for each outcome must agree, in other words you may
choose (a) and (d) as the answer or (b) and (c). Other combinations
would be self cancelling and therefore incorrect.

No advanced physics, no references to abstruse web sites, just a simple
experiment that we can all do and probably have done by chance many
times.

--
Asha
nature.opcop.org.uk
Scotland

Asha, the correct pair are a and c. In the case of both the ice cube and the kettle the radiation from your finger does not change. So how can it be an agent? It is the radiation from the ice cube and the kettle which is causing the temperature of your finger to change.

If you have a basin of water at room temperature and add cold water to it, it will cool but eventually return to room temperature. If you add hot water to the basin the water will warm and eventually return to room temperature.

If you place your finger below a kettle, to prevent it being affected by convection, it will feel warm because of the warm radiation, and if you place it above and ice cube it will feel cold because of the cold radiation.

WHAT I AM SAYING IS THAT KETTLES EMIT WARM RADIATION AND ICE CUBES EMIT COLD RADIATION (Caps lock got stuck). It is as simple as that.

A reason why my critics find this to understand is that the power emitted by a blackbody depends on the fourth power of its temperature. Thus a boiling kettle emits at 373^4 and an ice cube at 270^4. My finger is at say 300K and emiting at 300^4. The heating effect of the kettle is 19 - 8.1 = 10.9 compared with the cooling effect of the ice cube which is 5.3 - 8.1 = - 2.8 a very much smaller effect. In fact I doubt if anyone has noticed the effect of radiation, from an ice cube except you of course :-)

However, please let's not start this debate all over again. If there is anyone who does not want to believe that ice cubes emit cold radiation them it is alright by me.