# Light and spectroscopy - PowerPoint PPT Presentation

Light and spectroscopy

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Light and spectroscopy

## Light and spectroscopy

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##### Presentation Transcript

1. Light and spectroscopy

2. Demonstration • What information can we gather from the demo with the prism?

3. Demonstration So, what is white light made out of???

4. Visible Spectrum • The colors that we can see that make up white light • 400 – 700 nanometers • A quick aside on wavelengths and light… • Definition of a wavelength • Light as a wave vs. a particle • Light is a form of ENERGY! • Electromagnetic radiation – When a particle gets excited, it gives off energy in specific wavelengths. This energy is known as…

5. Visible Spectrum Continued • Only a PART of the electromagnetic spectrum • What on EARTH is this??? Ideas??? • The range of waves given off by particles arranged by their wavelength

6. The Electromagnetic Spectrum

7. Question? • Which side of the electromagnetic spectrum (EM spectrum for short) do you think has more energy? Why? Give evidence to support your answer.

8. Spectrums • Three types of spectrums • Continuous • Absorption • Emission • Depending on what happens to the object, it will give off waves of light that will categorize it in one of the three types of spectrums

9. Continuous Spectrum • What is an incandescent solid? • A solid that emits light because it is being heated. • When an object (of any phase) is heated, it gives off energy, in the form of LIGHT. when looked at with the correct tools you will see the visible spectrum. • The color of the object indicates its temperature. • Which is hotter – a red star or a blue star?

10. Absorption Spectrum • When an electron GAINS energy, it only can absorb energy at SPECIFIC wavelengths. • The wavelengths absorbed are SPECIFIC to EACH element / compound. • The wavelengths absorbed will appear as black lines, from the continuous spectrum. • Under what conditions does visible light produce an absorption spectrum? • When it is passed through a cool gas under low pressure.

11. Absorption Spectrum

12. Emission Spectrum • When an electron LOSES energy, it emits it, but only at SPECIFIC wavelengths, specific to the element • Those emitted will appear on the continuous spectrum, but the rest will remain black. • Under what conditions is an emission spectrum created? • When a hot gas is under low pressure.

13. Emission Spectrum

14. The Doppler Effect • What happens when an ambulance drives by with its sirens on? • This is the doppler effect! • Why does this happen? • Sound is a form of energy. The pitch of the sound has a specific wavelength. • Wavelengths are compressed as it approaches the observer, which makes the pitch higher. • Wavelengths are stretched out as they leave the observer, which makes the pitch lower.

15. How does this relate to light? • The same principle occurs with light waves, which are just another form of energy waves. • BUT , instead of hearing a higher / lower pitch, we might observe a higher / lower wavelength • What does it mean for an object to have a blue-shift? A red-shift? • What does it mean if the change in frequency is larger? (Think back to the ambulance, when does the pitch get the highest?)

16. Why is this important? • Light is a form of ENERGY • Heat is a form of ENERGY, and is given off at specific wavelengths of the EM SPECTRUM • Stars and other objects give off LIGHT AND HEAT, at specific frequencies • How could we use this information? • To determine the chemical make-up of stars • To determine the speed of galaxies, if moving at all, and their direction relative to us.

17. Chemical Make-up • What type of spectrum would a star give off? • Absorption spectrum • Why? • Each element in a star gives off specific wavelengths. Since the composition of each star will be slightly different, a spectrum given off by a star will be unique to it, just like a human’s fingerprint! • The color of the star (heat radiated off by the star) indicates its temperature.

18. Galactic Motion • Edwin Hubble, a famous astronomer, discovered that galaxies have a huge red-shift. • The further the galaxy was away from us, the larger the red-shift it had. • What conclusions can we make from this? • The universe is expanding!!!