Phys 1830: Lecture 8

1. Phys 1830: Lecture 8 • Tutorial/Office hour • Monday 3pm practice math and prepare for test. • 1 tutorial away! Use your iClicker even if you haven’t registered it with me yet! Do NOT register it online for this class. Quizzes are from the previous Friday and the current Monday and Wednesday. • Change of password • iclicker report on wall. • check the number on the clicker. • attach it to your name. • if your student number isn’t on the roster then email me with your name, iclicker number, and student number AND COURSE. No planetarium tonight. Contact Mr. Cameron.

2. Special Club! • Contact: • umastroclub@gmail.com University of Manitoba Astronomy Club Wonder about the origins of the Universe? Curious about black holes? Come out and help design the club activities! No need to be a geek  Meeting Wednesday at 5:30 pm in Allen 330

3. Quiz 2

4. 20,000° K 10,000° K 5000° K Intensity 2000° K 1000° K 500° K X-Ray Ultraviolet Visible Infrared Microwave Radio Phys 1830: Lecture 8 Test Friday Jan 30th In class. See online handout. Includes telescopes (Wednesday’s material) • Upcoming Topics • How the interaction of light and matter produce spectra. • Optical Telescopes • Radio Telescopes • B&W imaging workshop – scheduled Monday Feb 2 • Previous class: • Light, electromagnetic radiation • Wavelength, frequency • Thermal radiation • This class: • thermal radiation continued • Kirchhoff’s Laws • Spectra

5. The Interaction of light and matter. summary Recall column • Photons and matter interact creating spectra. • spectra can be used to assess • temperature (blackbody curve type spectrum) • processes that produce light or absorb it (i.e. what is going on) (Demo) (Animation)

6. Spectra Kirchhoff’s Laws summary Recall column • 3 empirical laws • Hot opaque body -> continuous spectrum • Cooler transparent gas between source& observer -> absorption line spectrum • Diffuse, transparent gas -> emission line spectrum

7. Spectra summary Recall column • This kind of spectrum (continuum) is caused by • Hot, low density gas • Hot, dense blackbody • Cooler transparent gas

8. Spectra • Our sun and other stars have an atmosphere. Imagine that you are in a spaceship far above the Earth’s atmosphere. Which of the following spectra would you observe when analyzing sunlight? • Continuum rainbow-like spectrum • Dark line absorption spectrum • Bright line emission spectrum

9. Spectral Finger Prints Solar Spectrum • Note that the emission lines for the lab spectrum of iron are at the same wavelengths of the absorption lines of iron in the sun. • We can use line spectra to determine the chemical elements in an object.

10. Interaction of Light and Matter: How are line spectra created? Photons of light interact with atoms and molecules. • Atoms consist of: • Electrons (negative charge) • Nuclei (balance charge of electrons) • Protons (positive charge) • Neutrons (neutral charge) • Molecules are a group of 2 or more atoms.

11. Interaction of Light and Matter • Hydrogen is the simplest atom. • 1 electron and 1 proton. • Classical picture is that the electron is in an orbit. • Contemporary picture represents the electron as a cloud. • Orbits are really energy levels.

12. Interaction of Light and Matter Hydrogen Atom Energy Levels • Every chemical element has its own specific set of energy levels. • Each energy level is associated with a wavelength.

13. Interaction of Light and Matter Creating spectral lines at visible wavelengths • There are specific (quantized) energy levels. The level with the lowest energy is the ground state. • How does the electron get excited into a state with higher energy? • By interactions between photons and matter.

14. Interaction of Light and Matter: Creating spectral lines at visible wavelengths • The electron can shift between energy levels by absorption and emission of photons.