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Types of Spectra. Spectra. Most of you have seen light passed through a prism and separated into a rainbow of colors. Today you will use a different device to get a separation of colors. This device is known as a diffraction grating .

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Presentation Transcript
spectra
Spectra
  • Most of you have seen light passed through a prism and separated into a rainbow of colors.
  • Today you will use a different device to get a separation of colors.
  • This device is known as a diffraction grating.
  • The diffraction grating is in the spectroscope that will be used to analyze the colors in various light sources.
  • Your lab instructor will now demonstrate the use of a diffraction grating.
slide3
A picture of the spectroscope that you will use in this lab appears below. Also shown is a view of the interior.
slide4
When white light is viewed through a diffraction grating, a continuous spectrum will be produced.
  • It looks like this
  • It is continuous because all visible frequencies of light are present.
  • Continuous spectra arise from incandescent solids, liquids, and even gases when at high pressure.
slide5
A glowing, low density gas, such as a neon sign, produces a discrete emission spectrum.

This type of spectra is seen as having individual lines of different colors.

The colors that are emitted by an excited atom are characteristic of that particular kind of atom.

They represent a unique set of energy levels (electron orbits) for that kind of atom.

These unique sets of energy levels are predicted by quantum mechanics, not classical mechanics.

As an example of the kind of spectra that you will see today, the discrete spectra of oxygen and carbon appear on the next slide.

slide6

Oxygen

Carbon

fluorescent lamps
Fluorescent Lamps
  • Primary excitation - electron collisions with low pressure Hg vapor, UV given off
  • Secondary excitation - UV photons absorbed by phosphors. Phosphors fluoresce emitting visible light.
  • Remember that the visible light from the excited mercury vapor is also emitted.
slide8
You will now receive further explanation on the use of the spectroscope and the procedures of today’s experiment.