##### Definition:

Stefan Boltzmann Law is also known as Stefan's Law. It helps to resolve the unknown quantity between radiation emitted by the body, temperature and the surface area. This law illustrates that, the energy radiated by a blackbody radiator per second per unit area is proportional to the fourth power of the absolute temperature power radiated from a black body in terms of its temperature.

#### Formula:

Stefan Boltzmann Law (P) = ε σ A T^{4}
Surface area (A) = 4 π r^{2}
**Where,**
σ - Stefan's constant (5.67 x 10^{-8} W m^{-2} K^{-4})
P - Radiation Energy
A - Surface Area
T - Temperature
r - Radius
##### Example:

A Metal ball 3 cm in radius is heated in a furnace to 5000C. If its emissivity is 0.5, at what rate does it radiate energy?

##### Given,

Radius (r) = 3 cm
Temperature (T) = 500^{0}C
Emissivity (ε) = 0.5

##### To Find,

Radiation Energy (P)

##### Solution:

###### Step1:

First, calculate the Surface area of the ball (A),
A = 4 π r^{2}
= (4 x 3.142)(0.03 m)^{2}
= (12.568) (0.03 m) ^{2}
= 0.0113112 m^{2}

###### Step2:

Now, calculate the Temperature (T),
T = 500 ^{0}C + 273
T = 773 K.

##### Step3:

Finally, calculate the Radiation energy (P),
P = ε σ A T^{4}
P = 0.5 x 5.67 x 10^{-8} x 0.0113112 x (773)^{4}
**P = 114.37 W.**