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For Monday, Apr. 7

For Monday, Apr. 7. Reading: Sections 5.1, 5.2, 5.5, Math Tools 5.1 and 5.3 Assignments: Mini-Project #1 - Part 2 (due today) Mini-Project #4 (due Fri. Apr. 11). ABSORPTION. The Ring Nebula. EMISSION. 1 LIGHT-YEAR. THERMAL RADIATION. WAVELENGTH. Light Waves.

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For Monday, Apr. 7

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  1. For Monday, Apr. 7 Reading: Sections 5.1, 5.2, 5.5, Math Tools 5.1 and 5.3 Assignments: Mini-Project #1 - Part 2 (due today) Mini-Project #4 (due Fri. Apr. 11)

  2. ABSORPTION

  3. The Ring Nebula EMISSION 1 LIGHT-YEAR

  4. THERMAL RADIATION

  5. WAVELENGTH Light Waves … caused by accelerating electrial charges wavelength (λ): distance between successive wave crests different colors have different wavelengths: frequency (f): number of wave crests that pass per second units: number per second, or Hertz (Hz) for sound waves, frequency = PITCH speed of light (c): RED BLUE 700 nm 400 nm WAVELENGTH

  6. The Electromagnetic Spectrum visible light is just a small part of the entire spectrum:  increasing f decreasing

  7. Thought Question: What wavelength will radio waves from station “90 FM” have? (FM station frequencies are given in mega-Hertz, or 106 Hz.) (Enter the answer in m to two significant digits.)

  8. WAVELENGTH Light Waves energy (E): higher frequency  larger energy RED BLUE WAVELENGTH Thought Question: • Which has higher energy? • Red light • Blue light

  9. For Wednesday, Apr. 9 Reading: Section 5.3 Assignments: Mini-Project #4 (due Fri. Apr. 11) Homework #5 (due Mon. Apr. 14) LUNAR ECLIPSE: night of APRIL 14 (Totality 12:06 -1:24 AM)

  10. LIGHT INTENSITY LIGHT INTENSITY V I BG Y OR V I BG Y OR WAVELENGTH WAVELENGTH Spectrum SPECTRUM: a way of describing a MIXTURE of light: how intense are different colors? Roughly equal mixture of colors appears WHITE: Unbalanced mixtures are tinted by most intense colors:

  11. Thought Question: If I project dots of red and green light on the screen, what will you see where they overlap? • A yellow dot • A brown dot • A blue dot • A black dot • A white dot If I project dots of blue, red, and green light on the screen, what will you see where they overlap? • A blue dot • A brown dot • An orange dot • A black dot • A white dot

  12. The Importance of Spectrums • Atoms of each element … • absorb and emit unique combinations of colors AND work the same way across the universe • Spectrums can be used to: • identify chemicals • measure temperature • measure speeds

  13. Kinds of Spectrum CONTINUOUS INTENSITY ABSORPTION LINE INTENSITY EMISSION LINE INTENSITY V I BG Y OR 400 nm WAVELENGTH 700 nm

  14. Thought Question What kind of spectrum would you see if you were looking in the direction shown by the arrow? continuous (thermal radiation) spectrum absorption line spectrum emission line spectrum star transparent gas cloud

  15. Types of Spectrum star (source of thermal radiation – frequent collisions between electric charges) transparent gas cloud (can absorb or emit specific wavelengths of light – atoms absorb and release light on their own) WHAT YOU SEE: ABSORPTION EMISSION THERMAL RADIATION

  16. Observing a Spectrum SPLIT LIGHT BY WAVELENGTH (PRISMS, CDs) SELECT SPECIFIC WAVELENGTH RANGES (FILTERS) greyscale (lighter = more intense)

  17. Kinds of Spectrum CONTINUOUS:hot, opaque materials emit thermal radiation examples: light bulbs, you, stars (sort of) EXAMPLE GRAPH: INTENSITY V I BG Y OR WAVELENGTH

  18. Jupiter’s Moon Io

  19. Jupiter’s Moon Io

  20. Jupiter’s Moon Io VolcanoHot spot

  21. Star Colors

  22. For Friday, Apr. 11 Reading: Sections 5.6, 13.1, 13.2 and Math Tools 13.1, 13.2 Assignments: Mini-Project #4 (due Fri. Apr. 11) Homework #5 (due Mon. Apr. 14) LUNAR ECLIPSE: night of APRIL 14 (Totality 12:06 -1:24 AM)

  23. RED ORANGE YELLOW WHITE Thermal Radiation • hot, opaque objects radiate light in a way that depends only on temperature • as T increases: • light of all wavelengths gets brighter • wavelength of most intense light gets shorter (bluer) WHAT WE SEE BY EYE: BLACK (no visible light)

  24. Thermal Radiation Stefan-Boltzmann Law: brightness at surface of hot object (also called flux) (energy released per second per area) (a constant) FOR SAME AREA, HOT SURFACE RELEASES LIGHT FASTER ALL COLORS GET MORE INTENSE

  25. Thermal Radiation • thermal radiation is released at all wavelengths, but… Wien’s Law: most intense light is released at this wavelength: HOTTER=BLUER Sun: Blackbody Applet Blackbody Applet 2

  26. Temperature

  27. INFRARED VIEWS ON EARTH (FALSE COLOR) Police Video

  28. SATURN (FALSE COLOR: RED = INFRARED)

  29. Star Luminosity • luminosity (L): total amount of energy released per time • units: Watt (W): 1 W = 1 J / s • property of a star: its “power” Stars release THERMAL RADIATION: • brightness of each piece of surface only depends on temperature • Apply Stefan-Boltzmann Law: flux from each piece of star’s surface star’s surface area

  30. Thought Question: The graph below shows the blackbody spectra for three different stars. Which of the stars is at the highest temperature? • Star A • Star B • Star C

  31. Thought Question: The hottest stars can be more than ten times hotter than the Sun at their surfaces. How much brighter (energy released per m2 per sec) would the surface of such a star be compared to the Sun? What would the peak wavelength of such a star be (in nm) if the Sun’s peak is at around 500 nm?

  32. Jupiter’s Moon Io

  33. Thought Question: When I pass a jug of clear blue liquid in front of the light bulb, what will happen? • The jug will make the violet, blue, and green light more intense. • The jug will make the yellow, orange, and red light more intense. • The jug will remove most of the violet, blue, and green light. • The jug will remove most of the yellow, orange, and red light.

  34. Kinds of Spectrum ABSORPTION LINE:transparent material in front of hotter opaque material examples: seeing stars through gas (like an atmosphere) light is removed by cloud EXAMPLE GRAPH: INTENSITY V I BG Y OR WAVELENGTH

  35. Sun hydrogen sodium magnesium iron

  36. Arcturus hydrogen sodium magnesium iron

  37. ORION NEBULA (about 24 light-years across)

  38. Kinds of Spectrum EMISSION LINE:hot transparent material in front of cool background examples: street lamps, fluorescent bulbs, interstellar gas clouds light is released by cloud EXAMPLE GRAPH: INTENSITY V I BG Y OR WAVELENGTH

  39. Thought Question: Which of the following patterns most closely resembles the pattern of lines you saw in the spectrum?

  40. Atoms NUCLEUS: contains almost all of an atom’s mass protons: positively-charged particles neutrons: particles with no charge ELECTRON CLOUD: electrical force keeps electrons near nucleus electrons: negatively-charged particles HYDROGEN HELIUM More protons in nucleus means: stronger electrical force electrons more tightly bound to atom (on average)

  41. Absorbing Light • Electron only absorbs light with correct amount of energy to move it to an allowed distance from nucleus ENERGY LEVELS: -1 2 UNITS OF ENERGY ABSORBED -3 ELECTRON -6 GROUND STATE WHAT HAPPENS IN ATOM: electron moves farther from nucleus

  42. Emitting Light • Electron releases exact amount of energy needed to drop it to a smaller allowed distance from nucleus -1 ENERGY LEVELS ELECTRON -3 3 UNITS OF ENERGY RELEASED -6 GROUND STATE WHAT HAPPENS IN ATOM: electron moves closer to nucleus

  43. Energy Levels electrons in atoms are only allowed to: • have specific amounts of total energy • transition to other allowed energy levels OR off the atom absorbed light will have characteristic E and : E=0 E4 n = 4 E3 n = 3 n = 2 E2 n = 1 E1 not allowed allowed

  44. Thought Question: The electrons in an atom can be in the energy levels shown below. If an electron is in the ground state (the level with an energy of -9 units), how many units of energy can the electron absorb and still remain attached to the atom? (Enter ALL possible correct answers as one number, then hit send.) 8 units 9 units 10 units

  45. E Hydrogen: 0 eV the simplest atom… -0.8 eV -1.5 eV -3.4 eV nlo = 2 nhi =3,4,5,… -13.6 eV nlo = 1 nhi =2,3,4,… Balmer lines:

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