Can you please explain in detail about stephens law and about the emmissivites..??

how a radiation occur when a black body is inside a core(hollow sphere) at certain temp??

Stefan's Law

STEFAN’S LAW => It states that the total amount of energy radiated per second per unit area of a perfect black body is directly proportional to the fourth power of the absolute temperature of the surface of the body i.e.

E ∝ T⁴

Or,

E = σ T⁴

Where σ  is the Stefan’s constant. Its value is 5.67 x 10^-8 Js^-1 m^-2 K^-4 in SI.

In case, the perfect black body at temperature T is placed in an enclosure at temperature T₀, then heat energy radiated per second per unit area is given by

E = σ (T⁴ – T₀⁴ )

In case, T ≥ T0 then above equation reduces to

E = e σ (T⁴ – T0⁴)

Where e is called the radiation emissivity of the surface. Its value depends upon nature of surface.