Black Body Radiation

Black body radiation refers to the spectrum of light emitted by a perfect black body. A black body is an idealized object that absorbs all incident radiation and emits radiation according to its temperature. When a black body is heated, it emits a continuous spectrum of radiation that depends only on its temperature. The spectrum of black body radiation has a characteristic shape, which is known as the Planck curve. The intensity of radiation at a given wavelength is given by the Planck law.

Effect of Wavelength on Monochromatic Emissive Power

The monochromatic emissive power of a black body refers to the amount of radiation emitted by the black body at a particular wavelength. The monochromatic emissive power of a black body depends on its temperature and the wavelength of the radiation. The relationship between the monochromatic emissive power and the wavelength of the radiation is given by Wien's displacement law.

Wien's displacement law states that the wavelength of the maximum intensity of radiation emitted by a black body is inversely proportional to its temperature. This means that as the temperature of a black body increases, the wavelength of the maximum intensity of radiation emitted by the black body decreases.

The relationship between the monochromatic emissive power and the wavelength of the radiation is also affected by the shape of the Planck curve. The Planck curve has a peak at a particular wavelength, which corresponds to the wavelength of maximum intensity of radiation emitted by the black body.

Effect of Increasing Wavelength on Monochromatic Emissive Power

When the wavelength of radiation emitted by a black body is increased, the monochromatic emissive power initially increases. This is because the radiation emitted at longer wavelengths has a higher energy than the radiation emitted at shorter wavelengths. As a result, the monochromatic emissive power initially increases with increasing wavelength.

Effect of Further Increasing Wavelength on Monochromatic Emissive Power

However, as the wavelength of radiation emitted by a black body is increased further, the monochromatic emissive power reaches a maximum and then decreases. This is because the radiation emitted at longer wavelengths has a lower energy than the radiation emitted at shorter wavelengths. As a result, the monochromatic emissive power decreases with increasing wavelength beyond a certain point.

Conclusion

In conclusion, the monochromatic emissive power of a black body initially increases with increasing wavelength, but then reaches a maximum and decreases beyond a certain point. This is because the energy of the radiation emitted by a black body depends on its wavelength, and the shape of the Planck curve determines the relationship between the monochromatic emissive power and the wavelength of the radiation.