1. Interaction of Light with Matter (1900) in the early 1900’s, there were three key behaviors associated with the interaction of light with matter that could not be explained… 1.the spectrum of radiation from a glowing hot object (blackbody radiation – basis of infrared goggles) 2.the emission of electrons from a metal when irradiated by light (photoelectric effect- now the basis of solar panels) 3.the absorption and emission of radiation by matter (color) we are going to briefly look at the issues and conclusions around the spectrum of radiation from a glowing hot object

2. 5000 K 3000 K lamp filament) Violet Green Yellow Red Infrared 6000 K (surface of sun)

3. 1500 K (red hot iron) 2000 K 3000 K Violet Green Yellow Red Infrared

4. Violet Green Yellow Red Infrared 1500 K (red hot iron) 2000 K 3000 K 5000 K 3000 K lamp filament) 6000 K (surface of sun) Violet Green Yellow Red Infrared As an object gets hotter, the spectrum of light given off shifts towards _______________ As an object gets cooler, the spectrum of light given off shifts towards _______________ Intensity goes ______________ as the temperature goes down. shorter wavelengths longer wavelengths down

5. Max Karl Ernst Ludwig Planck and The Particle Nature of Light (1900) in an effort to explain the radiation given off by hot objects, Planck made a revolutionary suggestion that electromagnetic radiation comes in quanta discrete amounts “little packets” pieces the energy of each “packet” E packet = h  Max Karl Ernst Ludwig Planck, (April 23, 1858 – October 4, 1947) was a German physicist who is regarded as the founder of the quantum theory, for which he received the Nobel Prize in Physics

6. Max Karl Ernst Ludwig Planck and The Particle Nature of Light (1900) light behaves as if it comes in packets light (radiation) is not continuous revolutionary we perceive the world as continuous - matter in space, time we sense that all places are possible as we move through space at any time …can have any energy revolutionary to suggest that radiation (energy) behaves in a discontinuous way light (radiation) can behave as waves as particles E packet = h  c =  Planck’s constant 6.626  10 -34 J·sec there was plenty of evidence that light behaves as as wave continuous discrete

7. Violet Green Yellow Red Infrared 1500 K (red hot iron) 2000 K 3000 K 5000 K 3000 K lamp filament) 6000 K (surface of sun) Violet Green Yellow Red Infrared the classical explanation for thermal radiation was based in: - charged objects in matter vibrate - thermally agitated charges can vibrate at any frequency - these charged oscillators emit radiation of that frequency - if the particles can oscillate at any frequency, then any frequency of radiation can be emitted accounts for continuous spectrum BUT using this model, the shape of the distribution could NOT be accounted for Hotter – vibrate faster, higher frequency (shorter wavelength)

8. Planck produced an empirical equation that fit the data mathematical contrivance concocted by “happy guesswork” OED - information developed by observation and experiment, rather than by deduction from theory - guided by mere experience without scientific knowledge

9. Planck then set out to develop a theory to explain his equation using the classical model that oscillators could vibrate at any frequency (therefore emit radiation at any frequency) he could NOT derive his equation theoretically so, he made a hypothesis that the emitted energy had to be thought of as “energy elements” or particles of energy based in part on work by James Clerk Maxwell and Ludwig Boltzmann (1860-1868) describing the distribution of particle speeds at thermal equilibrium (@ a given T) ……….. James Clerk Maxwell (Irishish) Ludwig Boltzmann (Austrian)

10. work by James Clerk Maxwell and Ludwig Boltzman describing the distribution of particle speeds at thermal equilibrium (@ a particular T) - it was known that if a set of molecules with any initial distribution of energies (speeds) was put into a constant temperature chamber, it would eventually redistribute into the Maxwell-Boltzman distribution at thermal equilibrium - the theoretical explanation for this distribution relied on being able to count the particles James Clerk Maxwell and Ludwig Boltzman Distribution of particle speeds at thermal equilibrium

11. Shapes similar Equations similar

12. -to apply the ideas of Maxwell and Boltzman for the theory describing the distribution of speeds of discrete particles at thermal equilibrium to the distribution of thermal radiation, Planck had to be able to “ count ” his energy - which means that it (the energy) had to come in discrete countable pieces - the energy of each energy element was proportional to the frequency of the oscillator - one of the terms that appeared already in his empirical formula …back to Planck… E packet = h 

13. Planck’s idea that radiant energy came in packets - particles of light - was not based in any physical evidence at the time. It was a mathematical convenience to consider radiant energy as “energy elements”. It was purely an assumption that allowed him to theoretically model the distributions of thermal radiation. ***** He himself did not believe or accept the particle nature of light.

14. In 1905, at the age of 23 (?) working as a technical assistant in the Swiss Patent Office in Bern, Switzerland - Albert Einstein - demonstrated the particle nature of light in his explanation of the photoelectric effect. Einstein was awarded the 1921 Nobel Prize in Physics for "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect" Albert Einstein (hey! that name is familiar)

15. Interaction of Light with Matter (1900) in the early 1900’s, there were three key behaviors associated with the interaction of light with matter that could not be explained… 1.the spectrum of radiation from a glowing hot object (blackbody radiation – basis of infrared goggles) 2.the emission of electrons from a metal when irradiated by light (photoelectric effect- now the basis of solar panels) 3.the absorption and emission of radiation by matter (color) Flaming Colors! Our next step towards understanding the structure of the atom is to investigate the interaction of light with matter…. COLOR