Wien's displacement law is useful for determining the temperatures of hot radiant objects such as stars, and it is also useful for a determination of the temperature of any radiant object whose temperature is far above that of its surroundings.
According to Kirchhoff's law, the ratio of emissive power to absorptive power is the same for all surfaces at the same temperature and is equal to the emissive power of a perfectly black body at that temperature.
And as for perfectly black body A = 1
Because in this the heat energy which is supplied to change the state is latent heat. Latent heat is hidden heat which does not raise the temperature but it has to be applied to change the state of the substance
Mechanical energy can be converted into heat. This important physical observation is known as the mechanical equivalent of heat. So, mechanical equivalent of heat states that motion(Work) and heat are mutually interchangeable and that in every case, a given amount of work would generate the same amount of heat, provided the work done is totally converted to heat energy.
It is because, only the top layer of the lake or river freezes. And as we know that the density of ice is lower than the water, so it comes at the top surface. As the thermal conductivity of ice is very less so the heat is not conducted by the lower water (in which fish is living). So it makes fish to survive even in icy water because heat does not flow from water to the atmosphere and the...