Q1: A diathermaneous substance __________ the thermal radiation completely.

ANS:C - transmits

"Transmits" in the context of thermal radiation refers to the ability of a material to allow thermal radiation to pass through it. When thermal radiation interacts with a diathermaneous substance, it is not absorbed, reflected, or blocked entirely. Instead, the substance allows the radiation to penetrate through it. This means that the thermal energy carried by the radiation can pass through the material and continue its propagation on the other side. This behavior is similar to how light passes through a transparent material such as glass. In the case of thermal radiation, the substance does not absorb the radiation to heat up itself, nor does it reflect the radiation back. Instead, it permits the radiation to travel through it, possibly experiencing some attenuation or reduction in intensity depending on the properties of the substance and the wavelength of the radiation. In summary, a diathermaneous substance "transmits" thermal radiation by allowing it to pass through without significant absorption, reflection, or blockage.