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what is a spectral line of a molecule?
can this be used to work out the wavelength and frequency of the incoming light?
can this be used to work out the wavelength and frequency of the incoming light?
Spectral Lines: Wavelength & Frequency Explained
- Thread starter joeyjo100
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In summary, spectral lines are narrow ranges of wavelengths of the electromagnetic spectrum that are used to identify the elements that emit them. They are created when light is passed through a prism and each line is identified by its wavelength.
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My understanding of it is its an extremely narrow range of wavelengths of the electromagnetic spectrum. You know those orange street lights that are everywhere? They're high pressure sodium lamps and that orange light is sodiums emission spectrum. If you shine a HPS lamp through a prism it won't separate into a rainbow like sunlight does, instead it'll separate into a handful of "spectral lines" which are different colours because they are different wavelengths. Its only when you combine all these wavelengths that you get that orange light that sodium gives off. Every element has its own unique emission spectrum. For example here's a mercury lamp:
as you can see mercury emits that bluish green light. If you shine that through a prism here's what you'd see:
thats mercurys emission spectrum and those bright lines of light you see are called spectral lines. As you can see its most intense spectral line is in the green region of the visible spectrum and its 2nd most intense one is blue. You can also see that they are not single wavelengths of light but are actually bands of wavelengths. Each band is called a spectral line. Heres a sodium lamp:
which emits that orange light. Shine that through a prism and you'll see something like this:
in that picture it looks like a single spectral line but its actually 2 spectral lines. They're both in the orange region of the visible spectrum:
so its not surprising that when they combine, the light looks orange.
I've heard people refer to them as "single wavelengths" but that makes no sense at all, if a single wavelength actually exists it would probably be narrower than 1 x 10-googleplex meters but saying there can be a single wavelength is like saying that if you keep counting you will eventually reach the largest number in the universe. If I'm not mistaken, different parts of a spectral line are more intense than others and there will be an area of the spectral line that is the most intense. This is the wavelength that they use to label the spectral line. For example sodiums 2 orange spectral lines in the visible region are said to be 588.9950nm and 589.5924nm. In reality there's no limit to how far you can zoom in so a computer could give you a number with a thousand numbers after the decimal so for example it'd be 588.99504367527234673474293568245723463246723587182469356934866... nm.
Heres a real informative article about sodiums emission spectrum:
http://unicorn.ps.uci.edu/H2A/handouts/PDFs/sodium.pdf [Broken]
according to that article, the 2 bright orange spectral lines are by far the most intense visible spectral lines that sodium emits. The brightest spectral line is twice the intensity of the 2nd brightest one and the 2nd brightest spectral line is 99.3% more intense than sodiums 3rd brightest visible spectral line. The ones you can see with the naked eye are only the spectral lines in the visible spectrum. Elements like sodium also emit spectral lines that you can't see. For example here's mercurys UV-Vis spectrum:
that intense spectral line at around 250nm is invisible because its in the UV spectrum:
that picture I posted at the top of the thread is a real picture, that's what you actually see when you shine mercury light through a prism. You can see the big crazy green spectral line at around 550nm and the less intense blue spectral line at around 440nm but to see that intense spectral line at around 250nm you'd need a pair of UV goggles.
EDIT: I'm getting a bit carried away with this reply here but I thought I should add this picture:
if you've never burned strontium before, look it up on youtube. It emits red light. As you can see strontium has a few spectral lines in the red region of the visible spectrum but it also has a few blue ones. The reason the light appears red is because its red spectral lines are way more intense than the blue ones. Take a look at mercurys UV-Vis spectrum again, you can see that the spectral lines in the yellow region are much less intense than its green and blue spectral lines which is why mercury light appears bluish green to the eye. I'll shut up now, as you can see I have a bit of an obsession with emission spectra lol.
as you can see mercury emits that bluish green light. If you shine that through a prism here's what you'd see:
thats mercurys emission spectrum and those bright lines of light you see are called spectral lines. As you can see its most intense spectral line is in the green region of the visible spectrum and its 2nd most intense one is blue. You can also see that they are not single wavelengths of light but are actually bands of wavelengths. Each band is called a spectral line. Heres a sodium lamp:
which emits that orange light. Shine that through a prism and you'll see something like this:
in that picture it looks like a single spectral line but its actually 2 spectral lines. They're both in the orange region of the visible spectrum:
so its not surprising that when they combine, the light looks orange.
I've heard people refer to them as "single wavelengths" but that makes no sense at all, if a single wavelength actually exists it would probably be narrower than 1 x 10-googleplex meters but saying there can be a single wavelength is like saying that if you keep counting you will eventually reach the largest number in the universe. If I'm not mistaken, different parts of a spectral line are more intense than others and there will be an area of the spectral line that is the most intense. This is the wavelength that they use to label the spectral line. For example sodiums 2 orange spectral lines in the visible region are said to be 588.9950nm and 589.5924nm. In reality there's no limit to how far you can zoom in so a computer could give you a number with a thousand numbers after the decimal so for example it'd be 588.99504367527234673474293568245723463246723587182469356934866... nm.
Heres a real informative article about sodiums emission spectrum:
http://unicorn.ps.uci.edu/H2A/handouts/PDFs/sodium.pdf [Broken]
according to that article, the 2 bright orange spectral lines are by far the most intense visible spectral lines that sodium emits. The brightest spectral line is twice the intensity of the 2nd brightest one and the 2nd brightest spectral line is 99.3% more intense than sodiums 3rd brightest visible spectral line. The ones you can see with the naked eye are only the spectral lines in the visible spectrum. Elements like sodium also emit spectral lines that you can't see. For example here's mercurys UV-Vis spectrum:
that intense spectral line at around 250nm is invisible because its in the UV spectrum:
that picture I posted at the top of the thread is a real picture, that's what you actually see when you shine mercury light through a prism. You can see the big crazy green spectral line at around 550nm and the less intense blue spectral line at around 440nm but to see that intense spectral line at around 250nm you'd need a pair of UV goggles.
EDIT: I'm getting a bit carried away with this reply here but I thought I should add this picture:
if you've never burned strontium before, look it up on youtube. It emits red light. As you can see strontium has a few spectral lines in the red region of the visible spectrum but it also has a few blue ones. The reason the light appears red is because its red spectral lines are way more intense than the blue ones. Take a look at mercurys UV-Vis spectrum again, you can see that the spectral lines in the yellow region are much less intense than its green and blue spectral lines which is why mercury light appears bluish green to the eye. I'll shut up now, as you can see I have a bit of an obsession with emission spectra lol.
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1. What are spectral lines?
Spectral lines are specific wavelengths of light that are emitted or absorbed by an atom or molecule. They are unique to each element or compound and can be used to identify and understand the composition of objects in space.
2. How are wavelength and frequency related in spectral lines?
Wavelength and frequency are inversely related in spectral lines. This means that as the wavelength increases, the frequency decreases, and vice versa. This relationship is described by the equation c = λν, where c is the speed of light, λ is the wavelength, and ν is the frequency.
3. What causes spectral lines to occur?
Spectral lines occur when atoms or molecules absorb or emit photons of light. These photons have specific energies that correspond to specific wavelengths and frequencies, resulting in the distinct lines seen in a spectrum.
4. How are spectral lines used in astronomy?
Spectral lines are used in astronomy to identify the composition of celestial objects, such as stars, planets, and galaxies. By analyzing the unique patterns of spectral lines, scientists can determine the chemical elements present in these objects and gain insights into their physical properties and evolution.
5. Can spectral lines be used to measure distance?
Yes, spectral lines can be used to measure distance through a process called redshift. As light from a distant object travels through space, it can become stretched or compressed, resulting in a shift in the wavelength of its spectral lines. By measuring this shift, scientists can calculate the distance to the object and gain a better understanding of the expansion of the universe.