1.The physical significance of ....... is that it tells us how fast heat is propogated or it diffuses through a material during changes of temperature with time.

2. According to Krichoff's law in thermal equilibrium absorptivity is equal to ........
3.In conduction heat transfers from...... temperature to low temperature.
4.In providing critical radius of insulation ....... & ........ are having significant importance.
5.Radiations are ....... waves.

Devi, Guru and Rafeeq,

Don't bother using different names. It is easier to address questions from the same person under the same name.

Also, many of these questions are standard definitions which you can obtain from Wiki pages after a little reading.

If you had read question 3, you will be pleasantly surprised how much you could do if you tried.

I do not know

1. The physical significance of thermal diffusivity is that it tells us how fast heat is propagated or diffused through a material during changes of temperature with time. To calculate thermal diffusivity, you need to know the thermal conductivity (k), specific heat capacity (c), and density (ρ) of the material. The formula for thermal diffusivity (α) is α = k / (c * ρ).

2. According to Kirchhoff's law in thermal equilibrium, absorptivity is equal to emissivity. Kirchhoff's law states that at thermal equilibrium, the emissivity of a surface is equal to its absorptivity for all wavelengths. This means that a body that efficiently absorbs radiation also efficiently emits radiation at the same wavelengths.

3. In conduction, heat transfers from a high temperature region to a low temperature region. Conduction is the transfer of heat through direct contact between two objects or within a material.

4. In providing critical radius of insulation, factors such as the thermal conductivity of the insulation material and the temperature difference between the inside and outside of the insulation are of significant importance. The critical radius of insulation refers to the point at which adding more insulation does not significantly reduce heat transfer.

5. Radiations are electromagnetic waves. Electromagnetic radiation includes a wide range of wave frequencies, including radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Heat can be transferred through radiation in the form of electromagnetic waves.