The radiations emitted from the black body are discrete over the full light spectrum. These emissions from atoms have specific characteristics. Over the full spectrum, the solids emit radiation. The peak of the spectrum can be determined by the temperature of the solid.
Hence, the blackbody is an ideal absorber of incident radiation. For a body to stay in a thermal equilibrium state, it must emit radiation equal to the amount of the radiation it absorbs. The body must act as a good absorber and a good emitter at the same time at an equal rate.
Blackbody Radiation. That is, if you were to compare two blackbodies, regardless of what wavelength of light you observe, the hotter blackbody will give off more light than the cooler one. The spectrum of a blackbody is continuous (it gives off some light at all wavelengths), and it has a peak at a specific wavelength.
If you think in terms of visible light, the hotter the blackbody, the bluer the wavelength of its peak emission. For example, the sun has a temperature of approximately 5800 Kelvin. A blackbody with this temperature has its peak at approximately 500 nanometers, which is the wavelength of the color yellow.
Blackbody Radiation. First, let's do a quick review of temperature scales and the meaning of temperature. The temperature of an object is a direct measurement of the energy of motion of atoms and/or molecules. The faster the average motion of those particles (which can be rotational motion, vibrational motion, or translational motion), ...
The energy that the blackbody absorbs heats it up, and then it will emit its own radiation. The only parameter that determines how much light the blackbody gives off, and at what wavelengths, is its temperature. There is no object that is an ideal blackbody, but many objects (stars included) behave approximately like blackbodies.
The peak of the blackbody curve in a spectrum moves to shorter wavelengths for hotter objects. If you think in terms of visible light, the hotter the blackbody, the bluer the wavelength of its peak emission. For example, the sun has a temperature of approximately 5800 Kelvin.
Our strategy will be to begin by studying the properties of the simplest type of object that emits light, which is called a blackbody . A blackbody is an object that absorbs all of the radiation that it receives (that is, it does not reflect any light, nor does it allow any light to pass through it and out the other side).
Figure 3.5: Two-dimensional plot of the spectrum of a blackbody with different temperatures, please note: the color of the curves on the plot is not meant to be indicative of the color of the object emitting that light.
The temperature of an object is a measurement of the amount of random motion (the average speed) exhibited by the particles that make up the object; the faster the particles move, the higher the temperature we will measure.
Other common examples are the filament in an incandescent light bulb or the burner element on an electric stove.