Max Planck Albert Einstein Louis de BroglieWerner Heisenberg Modern Physics 20 th & 21 st century Niels Bohr Relativity Energy-Mass Equivalence Uncertainty Quantum Mechanics

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Sodium spectrum

Hydrogen Atomic Energy Levels

Absorption Spectrum Fraunhofer

The PhotoElectric Effect

Threshold frequency, f o, is the minimum frequency of light needed to get electrons to leave a plate (photoemmission). Every metal has a different thershold frequency. It appears as the x-intercept in the last graph below. Work function Ǿ= h fo the minimum energy of light needed to get electrons to leave a plate (photoemmissi on

E=mc 2 In nuclear reactions, energy can be converted into mass and mass into energy. Fission: splitting an atom (WWII Bomb) Fusion: joining atoms (how the sun makes energy)

The Lorentz Factor Distances (space) contracts by this factor as you approach the speed of light.

Graphing shows that γ doesn’t grow much beyond 1 until you reach about ___% of the speed of light

Einstein applied the Lorentz factor to time. Thus, time _______s at high speed

…and mass…… ……increases So if you try to get something up to light speed, it just keeps getting heavier and harder to move.

Length Contraction – Equation Length contraction takes place only along the direction of motion. Section 26.4

Another Verification of General Relativity General Relativity predicts that a light ray passing near the Sun should be deflected by the curved spacetime created by the Sun’s mass. The prediction was confirmed by astronomers during a total solar eclipse. Section 26.8

Black Holes * were theorized from Einstein's theory of gravitation. * General relativity says gravity bends light and warps space and time. * Black holes are old, very dense, dead stars that attract like so strongly that nothing can escape their pull, not even light. * We think black holes may be at the center of many spinning galaxies, sucking stars in. * Time itself is radically altered near and in black holes.

Thought Experiment – Werner Heisenberg’s Uncertainty Principle A thought experiment for viewing an electron with a powerful microscope In order to see the electron, at least one photon must bounce off it. During this interaction, momentum is transferred from the photon to the electron. Therefore, the light that allows you to accurately locate the electron changes the momentum of the electron. Section 27.8

The Uncertainty Principle Mathematically, – It is physically impossible to measure simultaneously the exact position and the exact linear momentum of a particle. – Physics admits there are some things we simply cannot ever know, no matter what! Section 27.8

The Compton Effect Compton saw that X-ray photons collided with team particles in a cloud chamber, knocked electrons off the water molecules. Photons acted like particles in collisions. Energy and momentum were conserved. Section 27.5

Louis de Broglie 1892 – 1987 Found a way to describe electrons as waves in postulated that because photons also have wave and particle characteristics, perhaps all forms of matter have both properties. Section 27.6

de Broglie Wavelength and Frequency The de Broglie wavelength of a particle is The frequency of matter waves is Section 27.6

De Broglie: Everything Can be a Wave! p = h/λ Or λ= h/p

If λ > size of opening or obstacle wave behavior dominates: it transmits or refracts through, diffracts around and interferes. If λ < size of opening or obstacle Particle behavior dominates: it bounces off like a solid particle. There is always a % possibility of either happening, but some probabilities are so low to be essentially impossible, or so high to be a virtual certainty.

Calculate the DeBroglie wavelength of ……. an electron moving at 300,000 m/s. λ= h/p = h/mv = 6.6 x Js/(9.1x kg ) x(3x10 6 m/s) = 2.1 x m which is approximately the radius of an atom. So an electron will diffract through slits < m. Experiments show electrons diffracting through crystals and forming interference pattern.

Calculate the DeBroglie wavelength of ……. A 1 kg rock moving at 5 m/s. λ= h/p = h/mv = 6.6 x Js/(1kg ) x(5m/s) = 1.5 x m which is smaller the radius of an electron. So a rock would only diffract if you could get it to pass through slits < m!!! Its DeBroglie wavelength is so small, it will never act like a wave, unless …….you could get its speed down to m/s. λ= h/p = h/mv = 6.6 x Js/(1kg ) x( m/s) = 1.5 m in which case it would diffract if you through it through the door. But that is a speed slower than 1 meter every billion years, so it will never happen.

Electron’s Orbit The circumference of the electron’s orbit must contain an integral number of de Broglie wavelengths. 2 π r = n λ – N = 1, 2, 3, … Section 28.3

Particle accelerators have revealed that there are a LOT more particles inside the atom than protons, neutrons and electrons

The Standard Model of Matter Particle accelerators have revealed that there are a LOT more particles inside the atom than protons, neutrons and electrons The Large Hadron Collider (LHC ) in Switzerland is the most powerful accelerator in the world. It went online in Smashing particles together forces ousub-atomic particles we have never seen before.

The Standard Model of Matter