Q.Define athermanous substances and diathermanous substances.

[!TLDR] Diathermanous substances transmit heat radiation; athermanous substances block it (opaque to it). [!ANSWER] Diathermanous: transmits heat radiation (e.g. glass, dry air). Atherma …

A diathermanous substance is one through which heat radiation CAN pass -- for such a substance the transmission coefficient tr is not zero, and it is neither a particularly good absorber nor a particularly good reflector. Examples include glass, quartz, sodium chloride, hydrogen, oxygen and dry air. An athermanous substance, by contrast, is one that is largely OPAQUE to heat radiation -- it transmits essentially none of the incident thermal radiation (tr = 0), instead absorbing and/or reflecting all of it. Examp …

Recall the definitions in terms of the transmission coefficient tr, and give on …

Mixing up the two terms, or assuming 'diathermanous' means transparent to VISIBLE light (it specifically refers to thermal/heat RADIATION, and a substance can be diatherman …