Modern Physics
Reinventing Gravity
 Einstein’s Theory of Special Relativity
 Theorizes the space time fabric.
 Describes why matter interacts.
 The larger the mass the larger the curve in
the space time fabric.
 Objects that are far away have less
interaction
Duality of Light
 As seen earlier evidence showed that light
can be refracted by gravity.
 During an eclipse scientists were able to
photograph EM radiation from stars behind
the sun.
 The gravity of the sun bent the light.
Photoelectric Effect
(Quantum Theory of Light)
 When EM radiation hits an object and the object
emits electrons (EX. solar panel)
 The electron receives energy from the EM
radiation.
 They behaved like particles colliding containing a
mass and therefore a momentum.
 Einstein called these bundles of energy photons.
So is light a wave or a particle?
 Both are correct but also both are incomplete.
 Lights dual nature is to this day unexplained in full.
 Wave theory - a beam of electrons move as a wave
also.
 Particle theory - higher intensity should equal higher
energy electrons
 Actually higher frequency light yields higher
energy e’s
Animation
 E =hf or E=hc/
 E is the energy of the photon
 h is Planck’s constant (on PRT)
 f is the frequency of the light
Sample Problem #1
 Find the energy of a photon of violet light
with a frequency of 7.69x1014Hz.
 E = hf
 E = (6.63x10-34Js)(7.69x1014Hz)
 E = 5.1x10-19J
Sample Problem #2
 The wavelength of a certain color of light is
6.1x10-7m. What is the energy of the
photons of light?
 E=hc/
 E= ((6.63x10-34Js)(3.00x10 8m/s))/(6.1x107m)
 E = 3.26x10-19J
Physics and the Atom
 What happens when light hits an object but does
not impart enough energy to cause the object to
emit electrons?
 The Bohr model answers this
 Electrons with the least amount of energy are in
the ground state.
 If an electron absorbs energy it can transition to a
higher energy level called an excited state.
 For an electron to jump energy levels it must
absorb the exact amount of energy needed.
 The electrons quickly return to ground state and a
photon is emitted.
 Energy of photon is equal to the energy difference
between the excited state and the ground state.
 Ephoton = Ei - Ef
 We will study 2 elements, Mercury and Hydrogen
(PRT’s)
*******Energy is given in eV, needs to change to J
when using Einstein’s equations********
Sample Problem
 An electron in an excited hydrogen atom drops
from the second level to the first energy level.
Calculate the energy, and the frequency of the
photon emitted.
 Ephoton = Ei - Ef
 E = -3.40 - (-13.6)
 E = 10.2eV
 (10.2 eV)(1.6x10-19J/eV) = 1.62x10-18J
 E=hf
 f=E/h
 f = 1.62x10-18J/ 6.63x10-34Js
 f = 2.4 x1015Hz
Sample #2
 Is it possible for a Hydrogen atom to absorb
0.47eV? If so what energy level jump is this
associated with?
 n=4 -> n=6
 -0.38eV - (-.85eV) = .47eV
Subatomic Physics
 Nucleus
 Protons
 Positive charge
 Mass of 1u or 9.31x102MeV
 Neutrons
 Neutral charge
 Mass of 1u
 These are called nucleons
Binding Energy (mass defect)
 When comparing the mass of nucleus and the sum
of the particles that make it up, the mass of the
nucleus is less that the sum of the parts.
 Einstein theorized this missing mass was turned
into energy used to hold the nucleus together.
 Hence E=mc2
 E is energy
 m is mass
 c is the speed of light
 The energy becomes two forces in the atom.
Binding Energy Forces
 Strong Nuclear Force
 An attractive force that hold nucleons together. Or
else protons will repel.
 Only effective over very short ranges. 10-15
 Weak Nuclear Force
 The interaction between protons and electrons.
 Appears only during Beta decay as Neutron
become protons and emit electrons.
 These two plus gravity and electromagnetic
forces are the 4 known forces of the universe.
Elementary Particles
 Protons, neutrons and electrons were thought
to be the smallest particles until 1932.
 The invention of particle accelerators and
particle detectors have since led to the
discovery of over 200 new particles.
 They do not exist separately for very long.
 Particle detectors measure how gas and other
materials interact with these new particles.
Force Particles
 Theoretical physicists have proposed that the
forces are an exchange of particles between
two objects.
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Strong Nuclear Force - gluon particles
Weak Nuclear Force - W+W- Z gauge bosons
Electromagnetic Force - photon
Gravity - graviton
 All have been detected except for the graviton
Classifying Matter
 Open Reference tables to page 3
 All matter is either a hadron or a lepton.
 Leptons do not interact via strong nuclear force,
hadrons do.
 Leptons
 6 known - including electrons and neutrinos (no charge,
less mass than an electron, result of nuclear reactions
on the sun)
 Hadrons
 Split into Baryons and Mesons both made up of quarks.
Quarks
 6 quarks that carry a fractional charge.
 Each quark is a different flavor, up, down,
strange, charm, top, bottom.
 3 quarks combine to make a baryon such as a
proton (uud). Composed of 2 up quarks and 1
down.
 By charge: +2/3e + +2/3e + -1/3e = +1e
 All baryons must be made of quarks whose
charge equals a whole number(+ or - )
Anti-particles
 For each particle, there is a corresponding
antiparticle which has an opposite charge but
the same mass.
 Ex. Positron or anti-electron has the same mass
as an electron but an opposite charge.
 These particles only exist for short periods of
time. When they interact with their counterpart,
they may annihilate releasing photons and
gamma rays.
 Ex. Cosmic radiation
 Anti-particle or anti-matter has only been found
in particle accelerators
Mesons
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Composed of a quark and an anti-quark.
Less massive than baryons.
Always have a charge that is a whole number.
Exist for 10-8 - 10-9 s.
Grand Unified Theory (GUT)
 The physics on a large scale does not match the
physics on a quantum scale.
 Theories such as string theory are trying to tie the
two together in order to create a single theory that
describes the entire universe.
 Problem: string theory requires a minimum of 6
dimensions of which we only know 4.
Hypothetically up to 11 dimensions.