Spectroscopy
- 1. Spectroscopy Mrs.P.Kanmani, Assistant Professor, Department of Physics, V.V.Vanniaperumal College for Women, Virudhunagar
- 2. Spectroscopy • Spectroscopy pertains to the dispersion of an object's light into its component colors (i.e. energies). • By performing this dissection and analysis of an object's light, one can infer the physical properties of that object.
- 3. Light and Energy The wave speed of a light wave is simply the speed of light, and different wavelengths of light manifest themselves as different colors. The energy of a light wave is inversely-proportional to its wavelength; in other words, low-energy waves have long wavelengths, and high-energy light waves have short wavelengths.
- 5. Why Spectroscopy? Interactions of Light and Matter – The interactions determine everything we see, including what we observe in the Universe. When we look at the Universe in a different "light", i.e. at "non-visible" wavelengths, we probe different kinds of physical conditions -- and we can see new kinds of objects. For example, high-energy gamma-ray and X-ray telescopes tend to see the most energetic dynamos in the cosmos, such as active galaxies, the remnants from massive dying stars, accretion of matter around black holes, and so forth.
- 6. Why Spectroscopy? Visible light telescopes best probe light produced by stars. Longer-wavelength telescopes best probe dark, cool, obscured structures in the Universe: dusty star-forming regions, dark cold molecular clouds, the primordial radiation emitted by the formation of the Universe shortly after the Big Bang. Only through studying astronomical objects at many different wavelengths are astronomers able to piece together a coherent, comprehensive picture of how the Universe works.
- 7. Interaction of light and matter How do light and matter interact? • Emission • Absorption • Transmission – Transparent objects transmit light – Opaque objects block (absorb) light • Reflection or Scattering
- 9. Continuous Spectrum Continuous spectra arise from dense gases or solid objects which radiate their heat away through the production of light. Such objects emit light over a broad range of wavelengths, thus the apparent spectrum seems smooth and continuous. Stars emit light in a predominantly continuous spectrum. Other examples of such objects are incandescent light bulbs, electric cooking stove burners, flames, cooling fire embers.
- 10. Emission Spectrum Thee electron clouds surrounding the nuclei of atoms can have only very specific energies .Each element on the periodic table has its own set of possible energy levels. Atoms will also tend to settle to the lowest energy level. This means that an excited atom in a higher energy level must `dump' some energy. The way an atom `dumps' that energy is by emitting a wave of light with that exact energy.
- 11. Absorption Spectrum What would happen if we fired this special photon back into a ground state atom? The atom could absorb that `specially-energetic' photon and would become excited, jumping from the ground state to a higher energy level. If a star with a `continuous' spectrum is shining upon an atom, the wavelengths corresponding to possible energy transitions within that atom will be absorbed and therefore an observer will not see them.