# OCR B: Advancing Physics Chapter 17

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• Created by: Caraa
• Created on: 24-05-13 12:36
• Probing Deep Into Matter
• Key words and definitions
• See my other resources for a full list
• Rutherford's scattering experiment
• Most alpha particles went straight through
• Atoms are mostly empty space
• Some were deflected back at significant angles
• So the center of the atoms must be tiny but contain a lot of mass
• Alpha particles were repelled
• We know they are positive, so this means the nucleus must be too
• Atoms  are neutral over all
• Therefore there must be something negative outside the nucleus (Electrons)
• How it was conduced
• Alpha particles (2 neutrons 2, 2 protons) fired are thin foil of gold atoms
• Coulomb's law
• F = (kQq)/r^2
• Q/q = charge
• F = force
• r = distance
• k = 1/ (4 x Pi x Permittivity of material)
• Inverse square law applies
• Forces on q and Q will be equal and opposite
• Closest approach
• Closest distance that a particle can get to another particle
• r (closest approach) = (k.Q.q) / Kinetic energy
• Q and q are charges REMEMBER to use proton number!
• Remember about changing eV to Joules
• k = 1 / (4 x pi x permittivity of material)
• Conservation laws
• Momentum
• Energy
• Charge
• Mass
• Types of particles
• Particle tree (VIEW MY OTHER RESOURCES)
• Antiparticles
• Lepton/ Baryon number sign changed
• Opposite charge
• Particle and antiparticle annihilate to make energy. The oppose also works.
• Decay
• Beta-minus decay
• neutron -> proton + electron + antneutrino
• Particle accelerators
• Linear
• Alternating current applied to electrodes
• Timed so that particles are always attracted to the next electrode
• Cyclotron
• Circular
• Two semicircular electrodes used to accelerate particles across a gap.
• Alternating p.d applied
• Magnetic field used to keep them moving in a circle motion
• Particles spiral outwards
• Synchrotron
• Circular
• Electromagnets used
• Relativity
• For particles at high speeds
• No particle that has mass can move equal to or faster than light
• Rest energy = m.c^2
• Relativistic factor = Total energy / rest energy
• Electron energy levels
• Electrons in an atom can only exist at certain energy levels
• They can more down an energy level by emitting a photon