EMISSION OF ELECTROMAGNETIC RADIATION BY HOT OBJECTS:

 

EMISSION OF ELECTROMAGNETIC RADIATION BY HOT OBJECTS:

1. Emission of Electromagnetic Radiation by Hot Objects:
• Hot objects emit electromagnetic radiation across a wide range of wavelengths.
• At high temperatures, a significant portion of this radiation is in the visible region of the spectrum.
2. Temperature and Color Emission:
• As the temperature of an object increases, it emits different colors of light.
• Initially, it appears dull red, then becomes progressively redder.
• As it heats further, it emits white light and eventually blue light at very high temperatures.
3. Temperature and Intensity:
• The intensities of radiations at various wavelengths depend on the temperature of the emitting body.
• Red radiation is most intense at a particular temperature, while blue radiation is more intense at another temperature.
4. Variation Among Materials and Temperatures:
• Objects made of different materials and kept at different temperatures emit varying amounts of radiation.
5. Reflection, Absorption, and Transmission:
• When an object's surface is irradiated with light, it reflects some, absorbs some, and transmits some of the radiant energy.
• This happens because ordinary objects are generally imperfect absorbers of radiation.
6. Black Body Radiation:
• An ideal body that emits and absorbs radiation uniformly across all frequencies is called a black body.
• The radiation emitted by a black body is termed black body radiation.
7. Practical Black Bodies:
• In reality, there is no perfect black body, but materials like carbon black come close.
• A good approximation to a black body is a cavity with a tiny hole, which allows radiation to enter and eventually be absorbed by the cavity walls.
8. Black Body Properties:
• A black body is a perfect radiator of radiant energy.
• It is in thermal equilibrium with its surroundings, emitting the same amount of energy per unit area as it absorbs.
9. Dependence on Temperature:
• The intensity and spectral distribution of radiation from a black body depend solely on its temperature.
• As temperature increases, the intensity of radiation increases with shorter wavelengths dominating.
10. Maxima and Temperature:
• The curve representing intensity vs. wavelength reaches a maximum value at a particular wavelength.
• As temperature increases, this peak wavelength (maxima) shifts towards shorter wavelengths.
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11. Predicting Radiation:
• Numerous attempts have been made to predict the intensity of radiation as a function of wavelength for black bodies.

Hot objects emit electromagnetic radiation, and their color and intensity depend on their temperature. While an ideal black body is a perfect radiator and absorber, practical approximations exist. The spectral distribution of radiation from a black body is determined solely by its temperature, with higher temperatures leading to shorter-wavelength radiation. This phenomenon is the basis of black body radiation theory, which has been subject to various attempts at prediction and modeling.