Charge and Field

  • Created by: Taviline
  • Created on: 07-12-14 12:00

Electric Fields

  • All charged objects have a field
  • Coulomb's Law - formula in book 
  • If a positive force the particle will be repelled, if a positive force the particles will be attracted
  • Use of electric force constant - K 
  • Inverse square law - as the objects get closer the force becomes stronger at an exponential rate
  • Unlike gravity, elecric force can be positive and negative
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Electric Field Strength

  • force for each unit of charge
  • N/C
  • F=qE
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Radial Fields

  • Objects with charge at a single point - or can be modeled like that - such as a hollow charge sphere 
  • At any given point field strength = kQ/r^2 - forumla book
  • Inverse square law
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Electrical Potential Energy

  • amount of energy requierd to move an object from infinety to a distance r from the particle
  • attracted particles will have a negative value
  • Eelec = 0 at infinte distance
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Electrical Potential

  • the amoutn of electrical potential energy per unit of charge
  • measured in volts
  • Velec
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Milikan's Oil drop experiment

  • found that all charges are some muliple of e 
  • viscous drag - air resistance
  • for an object falling at terminal velocity all forces must be in equilibrium
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Charge Particles in a Magnetic Field

  • Force is acting at a right angle to current
  • F=ILB
  • F=QVB
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Motion of a charge particle in an electric field

  • CERN uses magnetic fields to bend particles
  • circular motion occurs due to a constantly changing current direction
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Particle Accelerators

  • when a charged is acclerated across a potential difference it gains kinetic energy
  • KE = qV
  • when at high speeds you need the gamma factor
  • Etotal = Erest + Ekinetic = gamma * m *c^2
  • Linear Accelerators - long evacuate tubes, series of alternating charged electrodes, alternating power supply - as particles are passed through the polarity is changed - electrodes are of increasing length as particle speeds up but AC supply doesn't
  • Circular Accelerators - bend particles with magnetic fields , radiate synchrotron energy making them less efficent - tighter circle more energy lost.
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