Charles Hakes Fort Lewis College1

Charles Hakes Fort Lewis College2 Chapter 2 Stefan’s Law

Charles Hakes Fort Lewis College3 Outline Mid-term grades due - If you receive a C- or below for your mid-term grade, please come by my office to discuss your situation. Stefan’s Law Spectroscopy

Charles Hakes Fort Lewis College4 Review Questions

Charles Hakes Fort Lewis College5 Which list is in the correct order of electromagnetic radiation wavelength, going from shortest to longest? A) infrared, ultraviolet, gamma, radio B) gamma, x-ray, ultraviolet, visible C) radio, infrared, visible, ultraviolet D) radio, x-ray, ultraviolet, visible E) red, violet, blue, green

Charles Hakes Fort Lewis College6 Which list is in the correct order of electromagnetic radiation wavelength, going from shortest to longest? A) infrared, ultraviolet, gamma, radio B) gamma, x-ray, ultraviolet, visible C) radio, infrared, visible, ultraviolet D) radio, x-ray, ultraviolet, visible E) red, violet, blue, green

Charles Hakes Fort Lewis College7 Which is correct A) wavelength / velocity = frequency B) wavelength / velocity = period C) wavelength * frequency = period D) wavelength * velocity = frequency

Charles Hakes Fort Lewis College8 Which is correct A) wavelength / velocity = frequency B) wavelength / velocity = period C) wavelength * frequency = period D) wavelength * velocity = frequency

Charles Hakes Fort Lewis College9 The biggest contributors to global warming are: A) Water vapor and carbon dioxide B) Methane and carbon monoxide C) Chlorofluorocarbons (CFCs), which destroy the ozone layer D) Argon and Helium E) Al Gore and Rush Limbaugh

Charles Hakes Fort Lewis College10 The biggest contributors to global warming are: A) Water vapor and carbon dioxide B) Methane and carbon monoxide C) Chlorofluorocarbons (CFCs), which destroy the ozone layer D) Argon and Helium E) Al Gore and Rush Limbaugh

Charles Hakes Fort Lewis College11 Photon energy The energy of a photon (a packet of light) is directly proportional to the frequency of the photon. High frequency means high energy Double the frequency means double the energy of the photon.

Charles Hakes Fort Lewis College12 Figure 2.9 Ideal Blackbody Curve

Charles Hakes Fort Lewis College13 Stefan ’ s Law Total energy radiated (from each m 2 of surface area) is proportional to the fourth power of the temperature (T) 4.

Charles Hakes Fort Lewis College14 Stefan ’ s Law Total energy radiated (from each m 2 of surface area) is proportional to the fourth power of the temperature (T) 4. And the Stefan-Boltzmann equation: F =  T 4 F is Energy Flux (Energy/area e.g. Watts/m 2 )  is the Stefan-Boltzmann constant

Charles Hakes Fort Lewis College15 Figure 2.10 Blackbody Curves Note the logarithmic temperature scale. For linear scale, go look at the “black body” section of: do.edu/ do.edu/ example - oven

Charles Hakes Fort Lewis College16 Small Group Exercise A pulsating variable star has a temperature ranging from 4000 K to 8000 K. When it is hottest, each m 2 of surface radiates how much more energy? recall: F =  T 4

Charles Hakes Fort Lewis College17 A pulsating variable star has a temperature ranging from 4000 K to 8000 K. When it is hottest, each m 2 of surface radiates how much more energy? A) (sqrt2)x moreB) 2x more C) 4x moreD) 16x more

Charles Hakes Fort Lewis College18 A pulsating variable star has a temperature ranging from 4000 K to 8000 K. When it is hottest, each m 2 of surface radiates how much more energy? A) (sqrt2)x moreB) 2x more C) 4x moreD) 16x more

Charles Hakes Fort Lewis College19 Group Activity You have just baked a cake at 175C, and a Pizza at 220C. How much more energy is radiated from the Pizza?

Charles Hakes Fort Lewis College20 Group Activity You have just baked a cake at 175C, and a Pizza at 220C. How much more energy is radiated from the Pizza? convert from C to K

Charles Hakes Fort Lewis College21 Group Activity You have just baked a cake at 175C, and a Pizza at 220C. How much more energy is radiated from the Pizza? convert from C to K use Stefan’s Law F=  T 4

Charles Hakes Fort Lewis College22 Group Activity You have just baked a cake at 175C, and a Pizza at 220C. How much more energy is radiated from the Pizza? convert from C to K use Stefan’s Law F=  T 4 compare values using a ratio (pizza/cake)

Charles Hakes Fort Lewis College23 How much more energy is radiated by the pizza at 220K than the cake at 175K? A) 1.11x more B) 1.26x more C) 1.47x more D) 16x more

Charles Hakes Fort Lewis College24 How much more energy is radiated by the pizza at 220K than the cake at 175K? A) 1.11x more B) 1.26x more C) 1.47x more D) 16x more

Charles Hakes Fort Lewis College25 Spectroscopy

Charles Hakes Fort Lewis College26 Figure 2.8 Electromagnetic Spectrum

Charles Hakes Fort Lewis College27 ROY G BIV

Charles Hakes Fort Lewis College28 ROY G BIV red orange yellow green blue indigo violet

Charles Hakes Fort Lewis College29 Spectroscopy Analysis of radiation that has been split into component colors… Continuous Spectrum Emission Spectrum Absorption Spectrum …and how matter emits and absorbs that radiation

Charles Hakes Fort Lewis College30 Figure 2.11 Spectroscope

Charles Hakes Fort Lewis College31 Spectroscopy Example - Continuous Spectrum

Charles Hakes Fort Lewis College32 Figure 2.12 Emission Spectrum

Charles Hakes Fort Lewis College33 Spectroscopy Example - Emission Spectrum Each element has a unique “fingerprint” (Emission Spectrum) Plot intensity vs. frequency

Charles Hakes Fort Lewis College34 Figure 2.13 Elemental Emission

Charles Hakes Fort Lewis College35 Spectroscopy Example - Emission Spectrum Each element has a unique “fingerprint” (Emission Spectrum) Note - Helium

Charles Hakes Fort Lewis College36 Spectroscopy Example - Absorption Spectrum

Charles Hakes Fort Lewis College37 Figure 2.15 Absorption Spectrum

Charles Hakes Fort Lewis College38 Figure 2.14 Solar Spectrum

Charles Hakes Fort Lewis College39 Figure 2.16 Kirchhoff ’ s Laws

Charles Hakes Fort Lewis College40 Kirchhoff ’ s Laws A sufficiently dense substance (solid, liquid, or gas) emits a continuous spectrum. A low-density hot gas emits an emission spectrum. A low-density cool gas absorbs certain wavelengths from a continuous spectrum, leaving an absorption spectrum.

Charles Hakes Fort Lewis College41 But where do those lines come from?

Charles Hakes Fort Lewis College42 Background At the end of the 19th century, many scientists believed that they had “discovered it all” and that only details remained to be filled in. (Like why are those spectral lines there.) Electromagnetic energy appears to come in “packets”, called photons. Particle nature of photons helps explain interactions with matter. Photon energy is directly proportional to frequency.

Charles Hakes Fort Lewis College43 Quantum Mechanics (How to build an atom)

Charles Hakes Fort Lewis College44 How to Build an Atom Components Proton - heavy, positive charge Neutron - heavy, no charge Electron - light, negative charge Number of protons defines element type (atomic number) Sum of protons and neutrons defines atomic weight

Charles Hakes Fort Lewis College45 How to Build an Atom Almost all atom mass is in the nucleus (protons and neutrons) Protons are held together by nuclear force. (Very strong, but very short range.) Protons (positive charge) make an “electromagnetic potential well.” (Attracts negative charges.) Electrons (negative charge) are attracted to the well and “fill it up” until you end up with a neutral atom.

Charles Hakes Fort Lewis College46 Figure 2.18 Modern Atom - note electron “ cloud ”

Charles Hakes Fort Lewis College47 Some Rules for Atoms No two electrons can be in the same state of the same atom at the same time. Only certain energy levels are allowed. Only photons with the same energy as the difference between allowed atomic states can be absorbed or emitted from an atom.

Charles Hakes Fort Lewis College48 Hydrogen Spectrum Transitions from excited state to ground state will emit ultraviolet light. Transitions from higher excited state to first excited state emit visible photons.

Charles Hakes Fort Lewis College49 Figure 2.19 Atomic Excitation

Charles Hakes Fort Lewis College50 Figure 2.20 Helium and Carbon Allowed energy levels are much more complex when multiple electrons are involved. Allowed energy levels are much more complex when multiple nuclei are involved (molecules).

Charles Hakes Fort Lewis College51 Figure 2.21 Hydrogen Spectra - molecular and atomic Atomic spectrum shows the Balmer lines (the “H” lines) - H , H , H  etc 

Charles Hakes Fort Lewis College52 Three Minute Paper Write 1-3 sentences. What was the most important thing you learned today? What questions do you still have about today’s topics?