Power is the rate at which work is done or energy is transferred. It is defined as the amount of work done per unit time. The SI unit of power is the watt (W) where 1 watt is equal to 1 joule per second. It can also be expressed as P = W/t.
Thermal properties of matter describe how matter reacts to temperature changes. It includes concepts such as thermal expansion heat capacity and heat conduction. Materials expand with heat and contract when cooled. The relationship between temperature and physical properties like length volume and pressure is also explored under this chapter for different states of matter.
Absorptive Power (A):
It is that fraction of the total incident radiation that a body absorbs. It is defined as the ratio of the energy absorbed by the body to the total energy incident on it.
A = (Energy absorbed) / (Total incident energy)
Emissive Power (E):
It is that amount of energy radiated per unit area by a body per unit time at some temperature. Its value depends upon the nature of the material as well as upon its temperature.
E = Energy emitted/area × Time
Emissivity (e):
It is the ratio of the emissive power of a body to the emissive power of a perfect black body at the same temperature. It varies between 0 and 1, with 1 being a perfect black body.
e = (E_body) / (E_black body)
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