on a domestic gas cooker the temperture in the hottest part of the flame is about 2200k.if salty eater is spilled in the flame then it becomes yellow-orange.measurements with a spectrometer show the presence of an emission line at 589n.
1) the solar spectrum shows an absorption line at 589nm rather than an emission line. explain why the solar absorption line is darker than the background while the flame emission line is brighter.
There is sodium vapor in the sun and it absorbs the energy at 589 nm coming from the sun.(I assume you meant nm and not just n.) That's why you get an absorption line at 589 nm. There is no sodium vapor on earth (or at least very very little) AND you don't have a continuum as you have in the sun. So the emission line is all you see on earth. Look up atomic absorption spectrophotometry and see how we measure the amount of sodium in a sample BY ABSORPTION (when we pass sodium vapor from a flame emission THROUGH a sodium vapor lamp and let the lamp absorb the energy of emission.
To understand why the solar absorption line is darker than the background while the flame emission line is brighter, we need to consider the concepts of absorption and emission spectra, as well as the temperature of the sources.
1) Solar Absorption Line:
In the case of the solar spectrum, where we observe an absorption line at 589 nm, the line appears darker because it is formed due to absorption of light at that specific wavelength by elements in the outer layers of the Sun's atmosphere, specifically the cooler photosphere. These elements in the photosphere absorb the incoming light at 589 nm, resulting in a dip or decrease in the intensity of the light at that wavelength. This absorption happens because the outer layers of the Sun's atmosphere are cooler than the source of light emitting from the core.
2) Flame Emission Line:
In the case of the flame emission line at 589 nm, the line appears brighter because it is formed due to emission of light at that specific wavelength by atoms or molecules present in the flame. When salty water is spilled into the flame, the heat causes the salt ions to dissociate into their various constituent atoms. These atoms then become excited by the high temperature of the flame, and as they return to their ground state, they emit light at specific wavelengths, including 589 nm. This emission occurs because the temperature of the flame is much higher than the temperature of the surrounding background, allowing for the atoms in the flame to reach excited states and subsequently emit light at that particular wavelength.
In summary, the solar absorption line appears darker than the background because it is formed due to light being absorbed by cooler elements in the Sun's atmosphere, whereas the flame emission line appears brighter because it is formed due to excited atoms emitting light at a specific wavelength in a hot flame.