electric fields

Cards (38)

  • charge is a fundamental physical property of matter that causes it to experience a force when placed in an electric field
  • like charges repel
  • opposite charges attract
  • air can be treated as a vacuum when calculating force between charges
  • for a charged sphere, charge may be considered to be at the centre
  • the magnitude of the electric force between two objects is much greater than the gravitational force between them
  • the constant ε0 known as the permittivity of free space
  • an electric field can be represented by electric field lines
  • electric field lines show the direction and relative magnitude of the force on a positive test charged placed in the force field
  • the direction of an electric field lines at a point gives the direction of the force that would be felt by the positive test charge at that point
  • electric field strength is a vector quantity
  • the electric field of a proton is an example of a radial field
  • the electric field strength at a point in the field is defined as the force per unit charge on a positive test charge placed at that point
  • the electric field strengths at a point in a field is independent of the charge placed there - it is a property of the field
  • two objects of different charge placed at the same point in an electric field will experience the same field strength, but will feel different forces
  • electric field strength is measured in newtons per coulomb
  • a uniform electric field exerts the same force per unit charge everywhere in the field. this is shown by the field lines being parallel and evenly spaced
  • an example of a uniform electric field is the field between two charged parallel plates
  • the equation E=V/D can be derived from considering the work done moving a charge between the two plates (Fd=QΔV)
  • if a charged particle enters a uniform electric field at right angles to the field it will feel a constant force parallel to the electric field lines. this causes the particle to accelerate at right angles to its original motion and hence it follows a curved path (a parabola)
  • if a positive particle enters a uniform electric field initially at right angles the particle will accelerate in the direction of the field lines
  • if a negative particle enters a uniform electric field initially at right angles the particle will accelerate in the opposite direction to the field lines
  • the resultant electric field strength is the vector sum (i.e direction must be considered) of the individual electric field strengths
  • the electric potential (V) at any point in an electric field is the work done per unit charge on a positive test charge when it is moved from infinity to that position
  • the value of electric potential is zero at infinity
  • electric potential is a scalar quantity
  • electric potential is measured in joules per coulomb, or more commonly volts
  • the electric potential difference (ΔV) between two points is the energy needed to move a unit charge from one point to the other
  • the work done in moving a charge across a potential difference is given by: ΔW=ΔW=QΔVQΔV
  • equipotential are surfaces of constant potential
  • equipotentials are always perpendicular to field lines
  • no work is done when moving a charge along an equipotential surface
  • the potential gradient at a point in an electric field is the change of electric potential per unit distance
  • the electric field strength is equal to the negative of the potential gradient
  • the quantity ΔV/Δx is known as the electric potential gradient
  • electric field strength can be found from the gradient of a V-r graph
  • ΔV can be determined graphically by finding the area under a E-r graph
  • the force that acts between two point charges in a vacuum is directly proportional to the product of their charges and inversely proportional to the square of their separation