6.2 - Electric fields

• An electric field

  A region of space where a charge will experience an electrostatic force
• Electric field

  Force per unit charge
• Coulombs law

  Force is proportional to the product of the 2 charges

  Force is inversely proportional to the separation squared
• Radial fields

  For a positive charge the field lines start at the centre and go out to infinity

  For a negative charge the field lines end at the centre of the charge and start at infinity

  
• Uniform fields

  Field lines are parallel and go from positive to negative

  
• Parabolic motion in electric fields

  A charged particle moving through an electric field will feel an attractive force towards the opposite charged plate

  This causes parabolic motion
• Equation for linear fields


  V/d
• Equation for work done

  Q x V
• Define electric potential at a point in space

  Force acting per unit charge in an electric field
• Motion of charged particles

  A charged particle moving through an electric field will be attracted towards the oppositely charged plate

  
• How can the motion of charged particles in an electric field be modelled?

  Projectile motion - The two components of velocity are independent of each other. The velocity perpendicular to the field is not affected, velocity parallel to the field is.
• Potential at a point in an electric field

  The work done per unit charge in moving a positive test charge from infinity to that point in the electric field
• Difference between gravitational and electric fields

  Gravitational Fields are always attractive, Electric fields can be attractive or repulsive
• Similarities between Gravitational and Electric fields

  Both follow the inverse square law for the force Point masses and point charges both produce a radial field Newtons law and Coulombs law formulae for force are similar Field strength is defined by force per unit charge/mass
• Permittivity

  The ability of a material to transmit an electric field (how easy the atoms become polarised
• Coulomb's Law


  The force between any two point charges is proportional to the product of their charges and inversely proportional to the square of the distance between them
• What is the effect of distance on the strength of the force?

  Greater distance = weaker force Represented by field lines being drawn further apart