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Spectroscopy

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Introduction

Chemistry Unit 2 Spectrometry Katie Bennett Spectrum Definition: The several coloured and other rays of which light is composed, separated by the refraction of a prism or other means, and observed or studied either as spread out on a screen, by direct vision, by photography, or otherwise. Introduction to Spectroscopy Spectroscopy is a complex art - but it can be very useful in helping scientists understand how an object like a black hole, neutron star, or active galaxy is producing light, how fast it is moving, and even what elements it is made of. A spectrum is simply a chart or a graph that shows the intensity of light being emitted over a range of energies. Spectra can be produced for any energy of light - from low-energy radio waves to very high-energy gamma-rays. Spectra are complex because each spectrum holds a wide variety of information. For instance, there are many different mechanisms by which an object, like a star, can produce light - or using the technical term for light, electromagnetic radiation. Each of these mechanisms has a characteristic spectrum. ...read more.

Middle

Below we see the spectrum, the unique fingerprint of hydrogen. These bright lines are called emission lines. Remember how we heated the hydrogen to give the atoms energy? By doing that, we excited the electrons in the atom - when the electrons fell back to their ground state, they gave of photons of light at hydrogen's characteristic energies. If we altered the amount or abundance of hydrogen gas we have, we could change the intensity of the lines, that is, their brightness, because more photons would be produced. But we couldn't change their colour - no matter how much or how little hydrogen gas was present, the pattern of lines would be the same. Hydrogen's pattern of emission lines is unique to it. The brightness of the emission lines can give us a great deal of information about the abundance of hydrogen present. This is particularly useful in a star, where there are many elements mixed together. Each element in the periodic table can appear in gaseous form and will each produce a series of bright emission lines unique to that element. ...read more.

Conclusion

From spectral lines astronomers can determine not only the element, but the temperature and density of that element in the star. Emission lines can also tell us about the magnetic field of the star. The width of the line can tell us how fast the material is moving, giving us information about stellar wind. If the lines shift back and forth, it means that the star may be orbiting another star - the spectrum will give the information necessary to estimating the mass and size of the star system and the companion star. If the lines grow and fade in strength we can learn about the physical changes in the star. Spectral information, particularly from energies of light other than optical, can tell us about material around stars. This material may have been pulled from a companion star by a black hole or a neutron star, where it will form an orbiting disk. Around a compact object (black hole, neutron star), the material in this accretion disk is heated to the point that it gives off X-rays, and the material eventually falls onto the black hole or neutron star. It is by looking at the spectrum of X-rays being emitted by that object and its surrounding disk, which we can learn about the nature of these objects. ...read more.

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Response to the question

The candidate has attempted to give a fairly detailed response and it is evident that they have taken the time to undergo independent research. This is shown by the inclusion of a bibliography at the end of the essay. By ...

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Response to the question

The candidate has attempted to give a fairly detailed response and it is evident that they have taken the time to undergo independent research. This is shown by the inclusion of a bibliography at the end of the essay. By taking the time to throughly research your topic, you demonstrate dedication and an interest in your subject.

Level of analysis

The candidate starts this piece for work by stating a definition, this can be useful when writing about a scientific topic, however the definition given is unclear, which makes me question the candidate’s understanding. In addition to this the candidate does not give a clear introduction. You should always introduce the topic you are discussing, a good introduction should introduce your essay title, state the topics you plan to discuss and engage the reader, which you can do by stating interesting facts or even a quote that is related to your set topic. By catching the readers attention, you ensure that they will invest time in reading all of your essay instead of skimming through it. In addition to this the candidate also fails to write any kind of conclusion, which is a mistake. You should always try to conclude your work. A good conclusion should summarise key points from within your essay and should include a personal response. This allows you to bring the essay to a close.

Quality of writing

The language used by the candidate is a little too simplistic for this level of qualification and very few technical terms are used. For example there is a point in the essay in which the candidate states that the electromagnetic spectrum covers all energies of light, they should have used the term electromagnetic radiation instead of word light which is misleading. This shows that the candidate’s level of understanding of these topics is only average. Furthermore there are some errors which punctuation and grammar.


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