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November 9

Black Body emissive power in medium

The black body emissive power in a medium $E_{m}$ is equal to the product of the square of its refractive index $n$ and the emissive power in vacuum $E_{v}$ with the formula:
$E_{m}=n^{2}E_{v}$ .
What does this mean in terms of the energy emitted, respecting the principle of conservation of energy and in the case where the energy is emitted in a vacuum, then enters a medium with refractive index $n$ ? Malypaet (talk) 23:16, 9 November 2024 (UTC)[reply]

Power is energy emitted over time. So energy is conserved as it is emitted more slowly. Heat energy turns into electromagnetic energy. Graeme Bartlett (talk) 10:15, 11 November 2024 (UTC)[reply]

Yes, but here, if you use the SI units in

Joules\cdot s^{-1}\cdot sr^{-1}\cdot m^{-2}

for emissive power as radiance, you have

E_{m}>E_{v}

. So, to conserve energy, you cannot use only the velocity for power, as you suggested. Malypaet (talk) 23:31, 12 November 2024 (UTC)[reply]

the most important unit is sr . In the vacuum the energy is distributed into all directions. In the medium it's too. But on entering the vacuum only certain directions are possible. In these directions the energy is concentrated. 176.3.66.65 (talk) 23:14, 22 November 2024 (UTC)[reply]