Question

what is physical meaning of emissivity and its unity​

Answer 1

Answer:

a measure of the ability of a surface to radiate energy; the ratio of the radiant flux emitted per unit area to that emitted by a black body at the same temperature.

Answer 2

The ratio of a surface's ability to emit radiant radiation to that of a perfect black body with the same area and temperature is known as emissivity.

Emissivity:

• The efficiency with which a material's surface emits energy as thermal radiation is measured by its emissivity.
• Infrared radiation, which cannot be seen by human eyes, as well as visible radiation (light) are both examples of thermal radiation, which is electromagnetic radiation.
• The thermal radiation from extremely hot objects can clearly be seen with the naked eye.
• A dimensionless constant, emissivity ranges from 0 to 1.
• Emissivity = 0 would be found in perfect reflectors.
• If an absorber were ideal, its Emissivity would be 1.

Radiative flux is expressed in joules per second (watts per square meter; W/m2) in the MKS unit system.

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