What is a black body?

According to Stefan's law of radiation, a black body radiates energy sigmaT^4 from its unit surface area every second where T is the surface temperature of the black body and sigma = 5.67 xx 10^-8 W//m^2 K^4 is known as Stefan's constant. A nuclear weapon may be thought of as a ball of radius 0.5 m. When detonated, it reaches temperature of 10^6 K and can be treated as a black body. Estimate the power it radiates

The decomposition of potassium chlorate (KClO_3) is a slow process. But the decomposition becomes fast in the presence of a black powder. Answer the following question : What is black powder?

What is a rigid body?

What is residual body?

Define a black body and explain how it can be realised in practice.