1. Chapter 4
Spectroscopy

3. Kirchhoff’s First Law
Hot, dense gases or solids produce a continuous spectrum.
Example: Light bulb filament
Continuous Spectrum

4. Kirchhoff’s Second Law
Hot, rarefied gas produces an emission line spectrum.
Example: Neon sign
Emission Line Spectrum

5. Kirchhoff’s Third Law
Cool gas in front of a continuous source of light produces an absorption line spectrum.
Example: The Sun
Absorption Spectrum

7. The Kirchhoff-Bunsen Experiment
These two scientists found that burning chemicals over an open flame resulted in a spectrum with bright lines.
They found that each chemical element produced its own characteristic pattern of bright spectral lines.

8. Structure of the Atom
Proton
Neutron
Electron
Quantized Energy Levels

9. Excitation There are two ways to get electrons excited.
Add Heat to the Atoms
This causes collisions.
Shine Light on the Atoms
Atoms can absorb light

10. De-excitation
When an electron makes a transition to a lower energy level a photon is released.

11. Emission Spectra
Spectral lines occur when an electron jumps from one energy level to another.
Each chemical element produces its own unique pattern of spectral lines.

12. Example Question
What two things can you do to atoms to cause electrons in the ground state to jump to the first excited state?
Add Heat
Add Light

13. Matching Questions Type of Spectrum Appearance
1. Emission Spectra a. All Colors
2. Continuous Spectra b. Dark Lines
3. Absorption Spectra c. Bright Lines

14. Matching Questions 1. Emission Spectra a. Hot Solids
2. Continuous Spectra b. Hot Stars
3. Absorption Spectra c. Hot Thin Gases

15. Spectra
Absorption occurs when a photon causes an electron to jump from a low energy level to a high energy level.
Emission occurs when a photon is emitted after an electron jumps from a high energy level to a low energy level.

16. Energy Carried by Light
“High frequency radiation carries proportionally more energy than low frequency radiation”. - Page 92

17. Compare these spectra. What do these spectra tell us about the star?
Spectrum of Hydrogen in Lab
Spectrum a Star
What do these spectra tell us about the star?

18. Measuring a Star’s Composition
Each atom absorbs a unique combination of wavelengths of light.
From this we can determine the composition of a star.
Star’s are composed of mostly hydrogen.

19. Compare these spectra. What do these spectra tell us about the star?
Spectrum of Hydrogen in Lab
Spectrum of a Star
What do these spectra tell us about the star?

20. Measuring a Star’s Motion
The spectral lines of a star moving away the Earth exhibit a redshift.
The spectral lines of a star moving toward the Earth exhibit a blueshift.
These shifts are caused by the Doppler effect.

21. Compare these spectra. What do these spectra tell us about the star?
Spectrum of Hydrogen in Lab
Spectrum a Star…..Day 1
Spectrum a Star…..Day 2
Spectrum a Star…..Day 3
Spectrum a Star…..Day 4
What do these spectra tell us about the star?

22. Mystery Star Properties
1. The star appears as a point of light through a telescope.
2. The absorption lines appear split and move over a
4 day period.
3. The brightness of the star also varies over 4 days.
Question: Why do you think the brightness of the
star is varying?
Answer: This could be an eclipsing binary star
system that cannot be resolved by a
telescope!

23. Matching Questions
1. The temperature of a star can be determined from its_____________.
2. The pattern of the absorption spectral lines for a star contains information about a star’s________________.
3. The Doppler shift of a star's spectral lines tells us something about the star’s_______________.
(a) composition
(b) motion
(c) color

24. End of Chapter 4