Q1: Planck's distribution law is valid for __________ bodies.

ANS:C - coloured

Planck's distribution law is generally applicable to black bodies. A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The spectral distribution of radiation emitted by a black body at a given temperature is precisely described by Planck's law. For colored or non-black bodies, Planck's law may not directly apply because these bodies do not absorb all incident radiation across all wavelengths equally. Instead, their absorption and emission properties vary with wavelength, leading to a different spectral distribution compared to that of a black body. While Planck's law itself is not directly applicable to colored bodies, concepts related to thermal radiation and black body radiation, such as Wien's displacement law and Stefan-Boltzmann law, may still be used to analyze the behavior of colored bodies under certain conditions. In summary, while Planck's law is valid for black bodies, its direct application to colored bodies is limited due to the complex nature of their absorption and emission properties across different wavelengths.