Light and Other Electromagnetic Radiation Topics Covered in Chapter 1 Structure of Atoms 2 Origins of Electromagnetic Radiation 3 Objects with Different Temperature and their Electromagnetic Radiation 4 Kirchoff s Spectral Laws 5 Bohr s Model of the Atom 6 Doppler Effect 1 A Subatomic Interlude 2 A Subatomic Interlude II 3 A Subatomic Interlude III 4 A Subatomic Interlude IIII 5 6 1 A Subatomic Interlude V Neutrino Detection Neutrinos are produced in the Weak Interaction for example Detecting neutrinos requires a different kind of a detector Neutrinos from the earth natural radioactivity Man made neutrinos accelerators nuclear power plants Astrophysical neutrinos Solar neutrinos Atmospheric neutrinos Relic neutrinos left over from the big bang 7 8 Neutrino Factoids Neutrino Detection II The earth receives about 40 billion neutrinos per second per cm2 from the sun About 100 times that amount are passing through us from the big bang This works out to about 330 neutrinos in every cm3 of the universe By comparison there are about 0 0000005 protons per cm3 in the universe Your own body emits about 340 million neutrinos per day from 40K Neutrinos don t do much when passing through matter Thus it is very difficult to observe neutrinos Neutrinos are observed by detecting the product of their interaction with matter e 9 Neutrinos reveal information about the Sun s core and have surprises of their own Neutrinos emitted in thermonuclear reactions in the Sun s core were detected but in smaller numbers 1 3 than expected Recent neutrino experiments explain why this is so Electron Muon 10 Determining the Speed of Light Galileo tried unsuccessfully to determine the speed of light using an assistant with a lantern on a distant hilltop Based upon conversion of electron neutrino to tau neutrino 11 12 2 Light travels through empty space at a speed of 300 000 km s In 1676 Danish astronomer Olaus R mer discovered that the exact time of eclipses of Jupiter s moons depended on the distance of Jupiter to Earth This happens because it takes varying times for light to travel the varying distance between Earth and Jupiter Using d rt with a known distance and a measured time gave the speed rate of the light 13 Light is electromagnetic radiation and is characterized by its wavelength In 1850 Fizeau and Foucalt also experimented with light by bouncing it off a rotating mirror and measuring time The light returned to its source at a slightly different position because the mirror has moved during the time light was traveling 14 d rt again gave c Wavelength and Frequency 15 The Nature of Light 16 Electromagnetism Electricity according to Gauss relates electricity to electric charge Faraday s Law In the 1860s the Scottish mathematician and physicist James Clerk Maxwell succeeded in describing all the basic properties of electricity and magnetism in four equations This mathematical achievement demonstrated that electric and magnetic forces are really two aspects of the same phenomenon which we now call electromagnetism 17 relates electric fields to magnetic fields Magnetism according to Gauss relates magnetism to electricity 18 3 Maxwell s Equations Because of its electric and magnetic properties light is also called electromagnetic radiation Visible light falls in the 400 to 700 nm range Stars galaxies and other objects emit light in all wavelengths Ampere Maxwell Law relates magnetic field to electricity Maxwell unifies electricity and magnetism into electromagnetism 19 20 An opaque object emits electromagnetic radiation according to its temperature Three Temperature Scales 21 22 Wien s law and the Stefan Boltzmann law are useful tools for analyzing glowing objects like stars A person in infrared color coded image red is hottest A blackbody is a hypothetical object that is a perfect absorber of electromagnetic radiation at all wavelengths Stars closely approximate the behavior of blackbodies as do other hot dense objects The intensities of radiation emitted at various wavelengths by a blackbody at a given temperature are shown by a blackbody curve 23 24 4 Wien s Law Wien s law states that the dominant wavelength at which a blackbody emits electromagnetic radiation is inversely proportional to the Kelvin temperature of the object 25 26 Stefan Boltzmann Law The Stefan Boltzmann law states that a blackbody radiates electromagnetic waves with a total energy flux E directly proportional to the fourth power of the Kelvin temperature T of the object E T4 27 Light has properties of both waves and particles 28 Light Photons and Planck Planck s law relates the energy of a photon to its frequency or wavelength E energy of a photon h Planck s constant c speed of light wavelength of light Newton thought light was in the form of little packets of energy called photons and subsequent experiments with blackbody radiation indicate it has particle like properties Young s Double Slit Experiment indicated light behaved as a wave Light has a dual personality it behaves as a stream of particle like photons but each photon has wavelike properties 29 The value of the constant h in this equation called Planck s constant has been shown in laboratory experiments to be h 6 625 x 10 34 J s 30 5 Chemists Observations Prelude to the Bohr Model of the Atom The Photoelectric Effect experiment explained by Einstein but performed by others What caused this strange result This is what Einstein won the Nobel Prize for 31 32 Each chemical element produces its own unique set of spectral lines 33 34 Kirchoff s First Spectral Law Kirchhoff s Laws Any hot body produces a continuous spectrum if it s hot enough it looks something like this digitally like this Intensity 35 Wavelength 36 6 Kirchoff s Second Spectral Law Any gas to which energy is applied either as heat or a high voltage will produce an emission line spectrum like this Kirchoff s Third Spectral Law Any gas placed between a continuous spectrum source and the observer will produce a absorption line spectrum like this or digitally like this or digitally like this Intensity Intensity Wavelength 37 Wavelength 38 Astronomers Observations 39 40 An atom consists of a small dense nucleus surrounded by electrons An atom has a small dense nucleus composed of protons and neutrons Rutherford s experiments with alpha particles shot at gold foil helped determine the structure 41 42 7 The number of protons in an atom s nucleus is the atomic number for that particular element The same element may have