DISUSUN OLEH

BLACK BODY RADIATION

Rahmawati Th. DiamantiIvone Pudihang

Recky LasutAulinda TambuwunDeyvita Montolalu

What is a Black Body ?

A black body is an ideal body which allows the whole of the incident radiation to pass into itself ( without reflecting the energy ) and absorbs within itself this whole incident radiation (without passing on the energy).

Black body radiation curves showing peak wavelengths at various temperatures

The graph shows: • As the temperature

increases, the peak wavelength emitted by the black body decreases.

• As temperature increases, the total energy emitted increases, because the total area under the curve increases. 

BLACK BODY RADIATION LAW

The Rayleigh-Jeans Law.

• It agrees with experimental measurements for long wavelengths.

• It predicts an energy output that diverges towards infinity as wavelengths grow smaller.

• The failure has become known as the ultraviolet catastrophe

4

2),(

ckT

TI

Planck's law of blackbody radiation

where• I(ν,T) is the energy per unit time (or the power)

radiated per unit area of emitting surface in the normal direction per unit solid angle per unit frequency by a black body at temperature T;

• h is the Planck constant;• c is the speed of light in a vacuum;• k is the Boltzmann constant;• ν is the frequency of the electromagnetic

radiation; and• T is the temperature of the body in kelvins.

Wien's displacement law• Wien's displacement law shows how the

spectrum of black body radiation at any temperature is related to the spectrum at any other temperature. If we know the shape of the spectrum at one temperature, we can calculate the shape at any other temperature.

• A consequence of Wien's displacement law is that the wavelength at which the intensity of the radiation produced by a black body is at a maximum, λmax, it is a function only of the temperature

Stefan-Boltzmann LawThe Stefan–Boltzmann law states that the power emitted per unit area of the surface of a black body is directly proportional to the fourth power of its absolute temperature:

where j*is the total power radiated per unit area, T is the absolute temperature and σ = 5.67×10−8 W m−2 K−4 is the Stefan–Boltzmann constant.

BENCANA ULTRAVIOLET

when the actual radiation emitted from a black-body was measured, it was seen not to shoot toward in infinite at the ultraviolet region of the electromagnetic scale (as the theories suggested), but rather to be highest toward the middle of the visible range of the spectrum, which seemed entirely counter-intuitive. It is for this reason that the discrepancy became known as The Ultraviolet Catastrophe.

CONCLUSION

Blackbody radiation does not depend on the type of object emitting it. Entire spectrum of blackbody radiation depends on only one parameter, the temperature, T

T H N K

Y O U

A